This error appears when performing Describe, using F4, on a table that is accessed by a Database Link (DB Link):
"ORA-00997 illegal use of LONG datatype".
The problem may be related to an Oracle 9.2 client issue.
If you are currently using an Oracle 9.2 client, try using a different Oracle client version to connect to your Oracle database. Once connected with a different Oracle client version, perform the F4 Describe function.
Try executing a DESCRIBE statement in Oracle's SQL*Plus. If you experience the same ORA-00997 error in SQL*Plus, then this is a problem related to the server and is not a Toad problem. Toad only acts as a graphical user interface (GUI) for Oracle, so Toad will display the same output that Oracle displays.