Check the below things when you counter error in a Source Qualifier :
- Always validate the source query before saving it and running the session.There may be syntax error.
- Check that the database login in both source qualifier and the corresponding session are the same.
- Test the SQL query in some client tools like SQL developer and confirm that the data is correct
- Check that all joins are proper in the Source Qualifier
- Also make sure that all the ports in select list from the Source Qualifier is taken into the next level
- The order in which the cols are given in Source Qualifier query should be in same order as its in the Ports tab
- Review the session log file if you need further information.