I recently upgraded to 4.1.1 and everything is running fine under Linux but PHP generates this message under windows:

[10-Jan-2002 09:56:15] PHP Fatal error:  Cannot find serialization handler wddx in Unknown on line 0

phpinfo() reports that WDDX is enabled.

This statement taken from the manual causes it:

print wddx_serialize_value("PHP to WDDX packet example", "PHP packet");