open (GB, ">>guestlog2.htm") or die "cant open data file: $!\n";
flock(GB, 2) or die "can't LOCK_EX data file: $!";
@gb = <GB>;
@gb2 = ("dgfdhgfdhgfdh");
foreach $line (@gb) {
    push (@gb2,$line);
    if($line =~ /INSERT_NEW_ENTRY/g){
        push (@gb2,"<b>Name:</b> $FORM{'Name'}\r<p>\r<b>Date:</b> <i>E
+RROR! Notify Me!</i>\r<p>\r<b>E-mail Address:</b> <a href=\"$FORM{'em
+ailaddress'}\">$FORM{'emailaddress'}</a>\r<p>\r<b>Comments:</b> $FORM
+{'Comments'}\r<hr>\r");
    }
}
seek (GB, 0, 0) or die "can't rewind $data_file: $!";
truncate(GB,0);
print GB @gb2;
close (GB) or die "can't close data file: $!";
[download]

You're opening the file for writing, but trying to read from it. Therefore your @gb array gets no data when you do:

@gb = <GB>;
[download]

Try opening the file for reading (or read/write) and see if it makes a difference.

--
<http://www.dave.org.uk>

"Perl makes the fun jobs fun
and the boring jobs bearable" - me

In this line, if($line =~ /INSERT_NEW_ENTRY/g){ there is no need for the "g".

--
$you = new YOU;
honk() if $you->love(perl)