When sending table from the Schema Browser to ER Diagram by right-clicking and selecting ER Diagram, Toad throws ORA-00904: invalid column name.
Toad needs the following tables for the launching the ER Diagram.
These tables in the 8i server are missing columns found in a 10g and above server. Specifically, these tables in 8i are missing columns char_length and char_used.
Waiting for fix in a future release of Toad for Oracle