One issue that I sometimes get is using the wrong Perl. I have different versions of Perl in different places (some on NFS shares so lots of machines can see the same Perl). If I install a module in one Perl (say /usr/local/bin/perl) but script (or path) uses another Perl (/usr/bin) then it may not have the modules. I have to take care to use the right version of the cpan (cpanp) tool for the Perl I want to use.

I don't know if this is the same in Windows.