Error event when you try to start the Microsoft Dynamics CRM E-mail Router Service in Microsoft Dynamics CRM 4.0

I’ve experienced this problem quite a few times. Email router stops working for no apparent reason. When you test the email router you get a warning message saying “Email Router Service is not Started”.

You also see this error message in the event view. 

“The E-mail Router service could not run the service main background thread.
The E-mail Router service cannot continue and will now shut down.
System.Configuration.ConfigurationErrorsException: The E-mail router service cannot access system state file Microsoft.Crm.Tools.EmailAgent.SystemState.xml. The file may be missing or may not be accessible. The E-mail Router service cannot continue and will now shut down.”

Looking around on the web I found quite a few solutions including advise to remove and re-install  the Email router. I found this KB that finally helped me resolve the issue.

http://support.microsoft.com/default.aspx/kb/954522