I've run into this enough times lately to warrant creating a visual walk-through of the fix. There is a KB article, if you like lots of words – but as always, a picture is worth a 1000 sandwiches...

KB Reference: http://support.microsoft.com/kb/923977

The Error (Event ID 53258)

MS DTC could not correctly process a DC Promotion/Demotion event. MS DTC will continue to function and will use the existing security settings. Error Specifics: %1

The Fix

Then reverse what you just did... Ridiculous ... I know)