I'm using the Linux VI Perl Toolkit on a Linux 2.6 kernel system running apache. assetinfo.pl is on this Linux web server as well as the assetinfo.xml. My VC is on a standard Windows 2003 server. I used the RegisterPlugin script you linked from the DOCs from the forums here. My command is almost the same as yours except I used my credentials and VC Server IP of course.
I guess its possible there could be a bug with the cookie module on Windows...seems unlikely though, but always possible.
To handle the ManagedObjectReference I had to use a bit of code :
my ($mo_type, $mo_value) = split(/:/, param('moref'));
my $vm_moref = new ManagedObjectReference( value => $mo_value, type => $mo_type);
my $vm_view = Vim::get_view( mo_ref => $vm_moref );
print "
VM Name: " . $vm_view->name . "\n";
print "
VM Annotation: " . $vm_view->summary->config->annotation . "\n";
undef $vm_moref;
My VMs are in an ugly state after toying around in my environment, so ignore the Unknown names