Here's a quick article on troubleshooting SEE-DC login fialures:
http://www.symantec.com/docs/TECH199466
What's the "inner exception" the message refers to? It sounds as if the service account under which SEE-DC is running has had some permissions revoked.
#EDIT#
Further to the above, has anything happened with regards to the SQL DB used by SEE-DC?
http://support.microsoft.com/kb/811889