Hello
Such a situation is possible because installation paths for perl modules can be a little bit mixed.
To example you have perl binary from rpm, then you decided to reinstall CPAN module from from its original source, then it's possible that further modules you are installing is copied in the little bit different paths then perl contains in @INC variable.

At least I saw this situation on my computer, when I tried to use existing perl from rpm and install mod_perl by manlually compiling its source. I would suggest you to reinstall perl, then apache, then mod_perl. I that case everything will be work fine for sure
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Alex