excel .xls error message after enable in..

[ttodd0450]

I use a spread sheet for excel.. and recently moved back from Office 2003 to Office 2000 and now when i open up an exisiting document in my spreadsheet .xls data base to up grade a spread sheet in excel, the moment it opens and i click on one key (enable in) i get this message:



the numbering add in must be loaded for optimal numbering and toolbar behavior . please load this add in into your library directory.

I have looked at the Go to Tools > Add-ins... and install the add-in required with my disc in hand,, but all add ins I check do not correct the problem.
Help !!

Thanks