Ever get this error from SQL Server Reporting Services when you consume a stored procedure and attempt to preview the report from the designer?
The data set "DataSetName" contains a definition for the field "FieldName". This field is missing from the returned result set from the data source.
The situation is that you receive this error even though the report designer and the data set designer clearly show it as a defined field. The reason for this can be complex, but in my situation I was consuming a stored procedure which returned the result set of a dynamic SQL Statement. This SQL Statement used 'SELECT *' instead of 'SELECT Column1, Column2...'. Once I corrected it to use the latter, everything worked. My thought is that when using a stored procedure (perhaps with dynamic SQL) it can't get a listing of the columns. Another factor in my case was that I was setting FMTONLY OFF. This allowed me to do an OPENROWSET on stored procedure results in another database.