GvCV no longer returns l-values from perl 5.13 onward.
I worked around that by instead running the GvCV_set commands.
Last time I looked at the code, on a Windows box those should load instead of the GvCV.
This might help:
http://mail-archives.apache.org/mod_...l.gmail.com%3E
edit:
this is more official:
http://search.cpan.org/~jesse/perl-5...longer_lvalues