Agreed. If the default perl on your path is different from /usr/bin/perl, that'd be why your script can't find the module you've installed. You then could either a) update your script to point to the version of perl that your shell is already using, or b) install your module for the version of perl that your script is using. Either way could be correct, I suppose, depending on your scripts needs.

You might also be able to do something like: #! /usr/bin/env perl to run your script with whatever perl your shell would use by default, but that way might lie madness...