So you've gone to a forum, created a thread and made a statement.
You don't say what you have tried, what you have changed, any event log messages other than that one, what issues you are having apart from this log entry or the set up.
You haven't even confirmed that you are using Exchange 5.5 and I thought this error was mainly 2003.
The logo in the corner says "Intelligent work forums for computer professionals." - the forums aren't THAT intelligent, we do need you to help.