There is not a lot of detail in the question (see the Support How-to for some tips on posting) but it sounds like you are probably adding data to a disconnected DataSet which
violates a unique constraint.
If the data you are trying to add does indeed violate the index then that what you are seeing is what I would expect. This question might also be of interest to you.
In general, the DataSet functionality is a thin wrapper on ADO.NET. e.g. ExecuteDataSet is really just doing a DataAdapter.Fill(). So, in most situations the approach you need to take is the same as if using a DataSet directly.
If you post more specific details then it would be possible to get a more specific answer.
Enterprise Library support engineer