User running office 2003 on exchange 2010 clicks to delete an email, nothing happens. After clicking a second time, the email deletes then a new window populates with "Unknown Error".

Changed the registry timeout on server running Exchange 2010 to extend the timeout, now emails after the change delete fine but any email delivered prior to that change still gets the unknown error.

Please review the Knowledge Base Article below from Microsoft. This should help resolve the error you are recieving.

http://support.microsoft.com/kb/814441

Hope this helps.

Mophead