Oh it is so logically, but you have to run in to it sometimes:
installing MOM 2005 in a testing environment, I left the MOMaction account with a blanc password. the error the install gave me seemed that there was no connectivity between the MOM server and the DC. even though I could do all things from this MOM server on the DC. It all came down to giving the momaction and MOMdas accounts a password.
I have not found a KB article about this, but it may be to straightforward a problem to write one.