The problem with WSDL::Generator is actually a class it uses, Class::Hook. The problem is specified in the Generator.pm perldoc:

=head1 CAVEATS

WSDL doesn't works only on perl 5.6 and not 5.8. UNIVERSAL::AUTOLOAD is broken in perl 5.8 and it is used by Class::Hook upon wich WSDL::Generator depends.

So, you can get it to work, presumably, by switching to perl 5.6. There is a more specific explanation of the problem (and a possible solution here)