Ok, I found the answer in this post: http://weblogs.asp.net/anjanaram/archive/2005/05/03/405434.aspx. Thank you AnjanaRam for this post.

from the post:

"For other system tables , it really doesn't matter if the stored procedure gets listed as 'user' or 'system' type. We would only need to create the Stored Procedure in master database with a prefix as 'sp_' and it works. But in order to access the sysfiles table from the right database, we need to explicitly change it to 'system' type.

And this can be done by running the Stored procedure ' sp_MS_marksystemobject.'

Execute sp_MS_marksystemobject 'system stored proc name'"