Add and Alias buttons are disabled

[Ruffneck]

Hi all,

I'm having some difficulty with a catalog, which a got from another consultant within the same company.

The catalog i'm using is a catalog created on a DB2 database. Now I'm trying to connect it with an Oracle database.
The structure of both database is the same. I had some problems while trying to verify the tables, but i have worked that out now. I can verify the tables and some of them (columns) are giving an X.

I want to remove these columns and replace them with the correct columns, but my Add and Alias buttons are disabled. Does anyone know how this can be fixed?Cognos can't do much for me now, because the Oracle database is an 8.01 and the don't support this anymore.