In the data source view, when you edit the SQL by yourself (right click on the table in the data source view, Replace table -> With new named query) be careful when using Oracle DB tables. When writing in the SQL the Oracle's table name with small casing, the SQL parser will add commas to the table name, making the SQL not work because the Oracle does not recognize this table name (with the commas).
Solution: Enter the table name with big casing, which will make the parser leave the table name as is. Also, remember: when creating or editing a named query always check and syntax, but also run the query and check that you get the desirable result before hitting the OK and saving the new named query.
by the way, I wonder: what were we doing if the Oracle was case sensitive?