Hello Athanasius, your request is reasonable... I hate the person who do not work to make understandable the code.
So I try and hope I have made better work.
I have created many packeges (as Agent.pm) from the command:

cd lib ; dbicdump -o debug=1 -o components='[qw(Helper::Row::ToJSON In
+flateColumn::Serializer InflateColumn::DateTime Helper::ResultSet::Se
+tOperations)]' MySchema::Master 'dbi:mysql:dbname=mydb' root ; cd ..
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The documentation created for the package Agent.pm is:
perldoc Agent

Agent(3)              User Contributed Perl Documentation             
+Agent(3)



NAME
       MySchema::Master::Result::Agent

COMPONENTS LOADED
       ·   DBIx::Class::Helper::Row::ToJSON

       ·   DBIx::Class::InflateColumn::Serializer

       ·   DBIx::Class::InflateColumn::DateTime

       ·   DBIx::Class::Helper::ResultSet::SetOperations

TABLE: "agent"
ACCESSORS
   id
         data_type: 'integer'
         extra: {unsigned => 1}
         is_auto_increment: 1
         is_nullable: 0

   profilo
         data_type: 'enum'
         default_value: 'Manutentore'
         extra: {list => ["Manutentore","Amministrativo","Admin","Admi
+nExt","Superadmin","Ente","AmExt","Ispettore"]}
         is_nullable: 1

   id_appalto
         data_type: 'integer'
         extra: {unsigned => 1}
         is_nullable: 1

   user
         data_type: 'varchar'
         is_nullable: 1
         size: 15

   pass
         data_type: 'varchar'
         is_nullable: 0
         size: 255

   disabled
         data_type: 'tinyint'
         default_value: 0
         is_nullable: 1

   note
         data_type: 'text'
         is_nullable: 1

   creation
         data_type: 'timestamp'
         datetime_undef_if_invalid: 1
         default_value: '0000-00-00 00:00:00'
         is_nullable: 0

   last_login
         data_type: 'datetime'
         datetime_undef_if_invalid: 1
         is_nullable: 1

   ts
         data_type: 'timestamp'
         datetime_undef_if_invalid: 1
         default_value: current_timestamp
         is_nullable: 0
PRIMARY KEY
       ·   "id"

UNIQUE CONSTRAINTS
   "idx_user"
       ·   "user"

RELATIONS
   controlloes
       Type: has_many

       Related object: MySchema::Master::Result::Controllo

   ispeziones
       Type: has_many

       Related object: MySchema::Master::Result::Ispezione



perl v5.18.2                      2015-05-26                          
+Agent(3)
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At the begin, in other package, I write the code:

...
sub master () {
    $Master ||= MySchema::Master->connect;
    return $Master;
}
...
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So, master->resultset('Agent') is the Agent MySQL table as Agent resultset. I can used the DBIx::Class::ResultSet methods as search_rs, ... without problems.
In my initial code posted, I can:

return $agent;
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or

return $agent->get_columns;
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(with 's' because I have loaded DBIx::Class::Row)
but I have the error already posted if in my code write

return $agent->profilo
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or

$agent->update({ last_login => \ " NOW()" });
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Why is there an error?
And, more important, why the same code not show error in old machine (and it is right)?

I do not understand. :-(
Thank you for any tips