Doesn’t make sense that only changing a namespace would make your WSDL valid assuming it was unique in the first place.
Use one of the WS-I Interoperability tests or XML Spy Enterprise to validate your WSDL.
Web services testing tools like SOAPSonar (free personal edition) and Parasoft SOATest will also verify that a WSDL is well-formed, semantically correct and adhereing to WS-I basic profile guidelines.