Problem:
While configuring Table Adapter query in ADO.Net Dataset, you may have received this error:The DataColumnMapping.SourceColumn is required to be unique. 'Column' already exists in the collection.
Solution:
Open the Dataset's xsd file with XML text editor. Search for the column name showing in the error. Manually remove the mapping column and then save the xml file.Hopefully you will have no error from now on.
