If you are running Microsoft Outlook 2003 on your exchange 2010 system and you as usual launch Outlook you may see that it fails to connect to the name of your exchange 2010 server and instead it tries to connect to;
Instance -d34234-sdfs-sdf23423-sdfs ( A GUID name ).See the example below.
You may also see that when you try to recreate the connection to exchange and do a checkname you see the connect to instance error again like this.
Other errors you may see are Office Outlook 2003 will not reconnect to the Exchange 2010 server. This may even happen with a simple restart of Outlook 2003.
This is a known issue with outlook 2003 and exchange 2010 see the Microsoft fix below.
Make sure that outlook 2003 is at service pack 2003.