Hi
Are you querying the data via the web service or via the database as this could be the difference. From what I understand, the dataset diffgram is used to track changes between the old data and the new data. What I believe the error is saying is that within the diffgram there is a set of data which doesn't match on name the dataset in the schema (form).
On this understanding, maybe the web service GetData is different from the web service SubmitData hence when getting the results from the query you are almost attempting to fit a square peg in a round hole.
So, in summary, I think this is down to the "shape" and "name" of the data is diffierent in one case from the other. Look into this and you will find the source of this error.
Sorry I cannot be more specific but on my rudimentary understanding this is what it sounds like.
Cheers
Adam