There has to be something wrong with your variable $text_mail. Is the attach method you showed in your original post called in the sub sendMail? Or somewhere outside? It could be a scoping issue.

Please insert the following in your program just before the attach and provide the result:

use Data::Dumper;

print Dumper(\$text_mail);

$msg->attach(
        ...
[download]

This will show exactly what is in $text_mail at the moment you call attach (it will even show hidden control characters should there be any)