i forgot all about this thing. it started cropping up in my environment but couldn't figure out why. after awhile, it finally dawned on me. the agent was reinstalled, but the computer table was never adjusted. yeah, i wish i was making this up. this happens when you monitor DCs in an untrusted forest or domain. here's the article. i particularly love the way it says this:
To work around this issue, install a separate MOM management group in each untrusted forest.
Note This issue has been known to be partially resolved by the following method. First, apply MOM 2005 SP1. Then, use the Active Directory Topology Discovery script to enable the server fully qualified domain names (FQDNs) to be added to the Computer table. However, when you use this method, most of the scripts will continue to log errors.
of course, it doesn't tell you how to resolve this. in the onepoint database, there's a table called "computer". there's a column in there called "fqdn". you have to specify the fqdn of the machine in question.