I know the dependancies are a little tricky with LWP::Simple, but I've scoured the source for LWP::Simple, LWP, and LWP::UserAgent to find somewhere among the source of those modules where an error called "INVALID ARGUMENT" could be decreed. I also double checked perllexwarn and perldiag, just to see if it's a known perl error message. I don't find it in any of those places either.