I remember there were some changes made to CGI.pm for mod_perl 2. I found this in the change log for CGI.pm:

 Version 3.08
    1. update support for mod_perl 2.0.  versions prior to
       mod_perl 1.999_22 (2.0.0-RC5) are no longer supported.
[download]

So you may need either a newer mod_perl or an older CGI module?

-Joe