Somehow when it's joining the two tables, it's not finding an equal link. Check out how it is linking table1 and table2. Sometimes it auto-picks all of the fields that it finds between the two tables that are named the same and it will try to make a join based on all of the fields. If the primary join between the tables is the accountno field, make sure that's the only link in there(delete any other ones). Or, if that is the only join, check and make sure that the accountno field really is exactly the same in the two tables(sometimes one could have a space character at the beginning or end of the string and that would cause the join to fail).