I caved in and did your work and it validated fine for me, both with \d and the more correct [0-9]. I suppose I guessed incorrectly about the pieces you didn't show us. Now you know why I don't like guessing.

Also check the XML with a hex editor. There might be non-printable characters or something in there.

Well here goes....

XML

<?xml version="1.0" encoding="UTF-8"?>
<instruction_request xmlns="http://www.finra.org/market_reg/admin_serv
+er/1.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.finra.org/market_reg/admin_server/1
+.0 admin_server.xsd">
    <request>
        <!-- The action to be performed => stop / start / reset   -->
        <action_request>
            <action>START</action>
            <!-- Application instance information. -->
            <instance_information>
                <!-- Application name. -->
                <application_type> app_type </application_type>
                <!-- The instance name. -->
                <application_name> some_app </application_name>
                <!-- This defines the environment:  QC / DEV / PROD --
+>
                <environment>QC</environment>
                <!-- This is the IP address of the application that is
+ -->
                <!-- being controlled in ASCII dotted-quad notation.  
+ -->
                <application_host_ip>123.123.24.56</application_host_i
+p>
                <!-- The hostname of the machine on which the machine 
+is exeucting. -->
                <application_host_name> somehost.finra.org </applicati
+on_host_name>
            </instance_information>
        </action_request>
    </request>
    <request>
        <!-- The action to be performed => stop / start / reset   -->
        <action_request>
            <action>STOP</action>
            <!-- Application instance information. -->
            <instance_information>
                <!-- Application name. -->
                <application_type> appname </application_type>
                <!-- The instance name. -->
                <application_name> app_instance </application_name>
                <!-- This defines the environment:  QC / DEV / PROD --
+>
                <environment>QC</environment>
                <!-- This is the IP address of the application that is
+ -->
                <!-- being controlled in ASCII dotted-quad notation.  
+ -->
                <application_host_ip>123.123.24.56</application_host_i
+p>
                <!-- The hostname of the machine on which the machine 
+is exeucting. -->
                <application_host_name> somehost.finra.org </applicati
+on_host_name>
            </instance_information>
        </action_request>
    </request>
    <request>
        <info_request>
            <action>GET_INFO</action>
        </info_request>
    </request>
</instruction_request>
[download]

XML Schema

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
    xmlns:admin_server="http://www.finra.org/market_reg/admin_server/1
+.0"
    targetNamespace="http://www.finra.org/market_reg/admin_server/1.0"
    elementFormDefault="qualified">

    <xs:annotation>
        <xs:appinfo xml:lang="English">This schema defines the XML str
+ucture that the admin server expects from the catalyst server.</xs:ap
+pinfo>
    </xs:annotation>
    <xs:element name="instruction_request">
        <xs:annotation>
            <xs:documentation>The root element. An instruction request
+ can contain 1 or more requests.</xs:documentation>
        </xs:annotation>
        <xs:complexType>
            <xs:sequence maxOccurs="1">
                <xs:element name="request" type="admin_server:request_
+choice_type"
                    maxOccurs="unbounded">
                    <xs:annotation>
                        <xs:documentation>A request must outline:
(1) The action to be taken.
(2) The application on which action is to be taken. (This can be optio
+nal if the action is to request information about all known applicati
+on instances.).</xs:documentation>
                    </xs:annotation>
                </xs:element>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
    <xs:complexType name="request_choice_type">
        <xs:choice>
            <xs:element name="action_request" type="admin_server:actio
+n_request_type">
                <xs:annotation>
                    <xs:documentation>The list of actions that are to 
+be carried out by the server.</xs:documentation>
                </xs:annotation>
            </xs:element>
            <xs:element name="info_request" type="admin_server:info_re
+quest_type">
                <xs:annotation>
                    <xs:documentation>The list of information requests
+. These are used to request information for specific application inst
+ances if specified. If application instances are not specified, the s
+erver replies back with information about all instances about which i
+t has information.</xs:documentation>
                </xs:annotation>
            </xs:element>
        </xs:choice>
    </xs:complexType>
    <xs:complexType name="instance_info_type">
        <xs:all>
            <xs:element name="application_type">
                <xs:annotation>
                    <xs:documentation>The type of application. 
</xs:documentation>
                </xs:annotation>
                <xs:simpleType>
                    <xs:restriction base="xs:string">
                        <xs:minLength value="1"/>
                        <xs:maxLength value="1024"/>
                    </xs:restriction>
                </xs:simpleType>
            </xs:element>
            <xs:element name="application_name">
                <xs:annotation>
                    <xs:documentation>The name of the application.</xs
+:documentation>
                </xs:annotation>
                <xs:simpleType>
                    <xs:restriction base="xs:string">
                        <xs:minLength value="1"/>
                        <xs:maxLength value="1024"/>
                    </xs:restriction>
                </xs:simpleType>
            </xs:element>
            <xs:element name="environment">
                <xs:annotation>
                    <xs:documentation>The environment in which the app
+lication is executing. The environment types are enumerated.
For instance: QC.</xs:documentation>
                </xs:annotation>
                <xs:simpleType>
                    <xs:restriction base="xs:string">
                        <xs:enumeration value="DEV">
                            <xs:annotation>
                                <xs:documentation>Development environm
+ent.</xs:documentation>
                            </xs:annotation>
                        </xs:enumeration>
                        <xs:enumeration value="QC">
                            <xs:annotation>
                                <xs:documentation>QC environment.</xs:
+documentation>
                            </xs:annotation>
                        </xs:enumeration>
                        <xs:enumeration value="PROD">
                            <xs:annotation>
                                <xs:documentation>Production environme
+nt.</xs:documentation>
                            </xs:annotation>
                        </xs:enumeration>
                        <xs:minLength value="1"/>
                        <xs:maxLength value="4"/>
                        <xs:whiteSpace value="collapse"/>
                    </xs:restriction>
                </xs:simpleType>
            </xs:element>
            <xs:element name="application_host_ip">
                <xs:annotation>
                    <xs:documentation>The IP address of the host on wh
+ich the application is executing.</xs:documentation>
                </xs:annotation>
                <xs:simpleType>
                    <xs:restriction base="xs:string">
                        <xs:maxLength value="15"/>
                        <xs:minLength value="7"/>
                        <xs:whiteSpace value="collapse"/>
                        <xs:pattern value="([0-9]{1,3}\.){3}[0-9]{1,3}
+"/>
                    </xs:restriction>
                </xs:simpleType>
            </xs:element>
            <xs:element minOccurs="0" name="application_host_name">
                <xs:annotation>
                    <xs:documentation>The hostname of the machine on w
+hich the application is executing.</xs:documentation>
                </xs:annotation>
                <xs:simpleType>
                    <xs:restriction base="xs:string">
                        <xs:minLength value="1"/>
                        <xs:maxLength value="1024"/>
                        <xs:whiteSpace value="collapse"/>
                    </xs:restriction>
                </xs:simpleType>
            </xs:element>
        </xs:all>
    </xs:complexType>
    <xs:complexType name="action_request_type">
        <xs:sequence>
            <xs:element name="action">
                <xs:annotation>
                    <xs:documentation>The action to be taken. The list
+ of valid actions are enumerated.</xs:documentation>
                </xs:annotation>
                <xs:simpleType>
                    <xs:restriction base="xs:string">
                        <xs:enumeration value="START"/>
                        <xs:enumeration value="STOP"/>
                        <xs:enumeration value="RESTART"/>
                    </xs:restriction>
                </xs:simpleType>
            </xs:element>
            <xs:element name="instance_information" type="admin_server
+:instance_info_type">
                <xs:annotation>
                    <xs:documentation>The unique application specifica
+tion on which the action is to be taken.</xs:documentation>
                </xs:annotation>
            </xs:element>
        </xs:sequence>
    </xs:complexType>
    <xs:complexType name="info_request_type">
        <xs:sequence>
            <xs:element maxOccurs="1" name="action">
                <xs:annotation>
                    <xs:documentation>The list of actions to be taken.
+ In these instance, these are read_only actions. The list of actions 
+are enumerated.</xs:documentation>
                </xs:annotation>
                <xs:simpleType>
                    <xs:restriction base="xs:string">
                        <xs:enumeration value="GET_INFO"/>
                    </xs:restriction>
                </xs:simpleType>
            </xs:element>
            <xs:element minOccurs="0" name="instance_information"
                type="admin_server:instance_info_type">
                <xs:annotation>
                    <xs:documentation>This is optional in this case. I
+f specified, the info is returned about the said instances.</xs:docum
+entation>
                </xs:annotation>
            </xs:element>
        </xs:sequence>
    </xs:complexType>
</xs:schema>
[download]

Still no error. I'm stuck on XML::LibXML 1.66 on this machine, but that shouldn't matter. libxml2 2.6.32 for the backend

>perl -MXML::LibXML -le"print for $XML::LibXML::VERSION, XML::LibXML::
+LIBXML_DOTTED_VERSION"
1.66
2.6.32
[download]

No problems on this machine either

$ perl -MXML::LibXML -le'print for $XML::LibXML::VERSION, XML::LibXML:
+:LIBXML_DOTTED_VERSION'
1.70
2.6.32
[download]

Same backend, so this was expected.

Thx Ikegami..... but I checked the schema in vim.... looks pretty plain text to me.... I also opened it in 0xED (Im on a mac but its a hex editor.... looks good...

Am investigating the issue... now I have never done this before but by providing a working example, would it be a good idea to post it to CPAN authors who have written this module? There aren't many examples out there for this module on CPAN. Will prolly help newbies like me.