So you get your web service client working nicely and deploy your code to Websphere only to find this ugly Websphere Exception:
[6/3/10 21:28:28:081 EDT] 00000035 Connection E com.ibm.ws.webservices.engine.client.Connection invoke WSWS3227E: Error: Exception: java.lang.IllegalArgumentException: argument type mismatch
From what I have read online, this can happen based on the webservices.jar file not being the most current one. I didn’t have that issue though, but what I did find was how Websphere’s classloader can cause this exception. I had setup a SharedLib for my new webservice JAR files but what I should have done was to include the JAR with my WAR file’s WEB-INF/lib and remove the entry from the Shared Lib. This seemed to fix this.