How do you drop a privilege from a non-existing object?

Hi,

I'm trying to revoke a privilege from sys.ext_tables.  We don't use the ext_tables anymore.  I don't know why it shows up as a sys object either, I think this was a mistake.  It was an external table that we no longer use.

I tried:

 revoke select on sys.ext_tables from <user>  force;

and received:

ORA-00942: table or view does not exist

I then tried creating a table and rerunning  the revoke statement with no luck.

Please help,

Faith