Sp_helpdb Error

Hi,
I have MOM 2005 installed to monitor all our sql servers. In one of the sql server on a specific db, I get error alerts when running the sp_helpdb error.

The error output is

"Server: Msg 515, Level 16, State 2, Procedure sp_helpdb, Line 53
Cannot insert the value NULL into column '', table ''; column does not allow nulls. INSERT fails.
The statement has been terminated."

I checked the sp_helpdb stored procedure and here is where it fails:

insert into #spdbdesc (dbname, owner, created, dbid, cmptlevel)
select name, suser_sname(sid), convert(nvarchar(11), crdate), dbid, cmptlevel from master.dbo.sysdatabases
where (@dbname is null or name = @dbname)

I understand this is a temporary table created by the stored procedure to insert all the db info.

I ran a query as follows:

select name, suser_sname(sid), crdate, dbid, cmptlevel
from master.dbo.sysdatabases

The output is

DB Name User Name Cr date db id cmpt
master sa2000-08-06 01:29:12.250180
model sa2000-08-06 01:40:52.437380
msdb sa2000-08-06 01:40:56.810480
RMSummaryNULL2002-06-13 16:40:32.203880
tempdb sa2005-11-29 19:10:48.450280

The problem is in RMSummary database and the "dbo" login does not
have a username.

How do I add a User Name "sa" to the DB Owner "dbo" for the RMSummary database?

I did try the following things with no success:

1. Try to delete the 'dbo' user in 'RMSummary' database so that
I can add a new login name as 'dbo' and username is 'sa'.
Error message is 'dbo' owns some objects and does not get deleted.
2. I tried sp_changedbowner but it does not work either.

Any help on this quickly is much appreciated.

Thanks
Murali