Maybe I'm way off here... but when I get that error message,
it's usually because I've typed $err = csDB::csErrorClass();
instead of $err = csDB::csErrorClass->new();
no, the csErrorClass module is in a module that's use'd by csDB, and it isn't an OO module at that. You'll notice further down the first thread on this post I mention that the Name of the sub is being exported successfully, but that apparently isn't a guarantee.