i agree mod_perl is not perl, i also have perl installed(it is mentioned), the problem isnt' a plesk related problem, it's the script that is having the issue, normal perl/cgi scripts run just fine. the information was given to help further narrow down a solution to the problematic script. I guess i'll just go with another solution that actually works under normal web-server environment conditions.
changing the entire structure of a webserver to suit the misguided needs of a poorly coded script is rediculous. Perhaps rather than flaming at the people asking for support, you should look into actually coding your script to work in more typical server / hosting environments.