The About plugins looks all right to me. How about your Edit/Preferences/Navigator/HelperApplications? Do you see an "application/x-perlplus" listed in there? Here's what you should set: 
Description of Type: PerlPlus Plugin
File Extension: .ppl
MIME Type: application/x-perlplus
Application to use: /usr/bin/perl $1

[download]
I have also successfully used the path to my perlplusplugin.so as the "application to use."

In reply to Re^11: PerlPlusPlugin: Security CGI problems by tall_man
in thread PerlPlusPlugin: Security CGI problems by basm101

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