Hi Amod,
Go to RSRT and perform 'Generate Report' check if you are able to see a different error message.
Go to the DSO check if its in correct Active status. Perform RSRV checks on the DSO. there could be a problem with your DSO definition.
if all seems fine then try to create a test query on a different infoprovider with same conversion. check if issue persists then there is problem with conversion if not then problem with infoprovider.
Hope this helps.
-swati.