Oracle 7 / TTable / IndexName for secondary index searches

I have inheited an app which is attempting to search a seondary index
of an Oracle 7 table (BDE 5.01), ussing a TTable and setting IndexName
to an apparently valid Oracle index name.

Everything works fine when the database owner attempts this, but when
any other user attempts to set the IndexName, an exception occurs
which states "Index does not exist"....

Obviously I could use a TQuery with ORDER BY <secondary index>, but
I'm sure you'll appreciate that's not the point.....

Any suggestions?

Thanks in advance

Ian Turner