You might want to try another list even a sample.
The issue is that the GUID is not being resolved properly. So if you are sure the GUID is right then it probably is that you are refering to the wrong site.
One thing I thought of is the data connection you are submiting with.. You need to navigate to the lists.asmx for the specific subsite where your list is located. The top level site will not work. I am using a team site list so I have to go to the
http://server/teamsites/XX/_vti_bin/lists.asmx?WSDLI am wondering if you are not drilling down to the right web service.
Just a thought otherwise it is probably one of those start over and create a working sample and go from there.