Error: The server instance specified was not found

Please post the code from the event, that might helpexplaining the error.

Managed to solve this by adding a new identity (host header) to the affected (default) website in IIS. The problem exists because we are accessing the portal using a DNS alias instead of the server name.

There is a KB article from Microsoft that explains this http://support.microsoft.com/?kbid=832816

Thanks!