Why do you think installation of WWW::Mechanize failed? The error you encounter is a runtime error at line 13 of your script. That implies that all the calls to that module above it, have actually succeeded — or at least, not made the module barf. Heck, even the $agent->links call, on the right of your grep block, must have returned some values or you wouldn't have gotten this far.

And ikegami pinpointed the cause of your problem. A non-existing method name, that's a runtime error, as methods can even be created (by AUTOLOAD) on the fly.

Conclusion: unless the exact same script works on another computer, and I sincerely doubt that, the module most likely will have been properly installed.