You no give enough information. Is it windows form or asp.net form?
I fetch slimier type of problem before.That is happen for use long integer data.Some time its happen for not correctly white dataset. So first check data type and white dataset like given example.
var ds = new DataSet(datasetName;);
var query ="Your SELECT Query";
ds.Tables.Add(dataTable);
ds.WriteXmlSchema(@"../../DataSetFile/DataSet.xsd");
I think its helpful for you.
thanks.