I've installed UR6 on a couple of server farms so far with not issues but today I encountered a problem that I'd not seen before.
The server UR6 install worked fine, but the Organisation still showed version 5.0.9688.1533 which is UR5 rather than the expected 5.0.9690.1992. Using File->About Microsoft Dynamics CRM, the version showed as (5.0.9690.1992) (DB 5.0.9688.1533)
Updating should have been simply a case of using Deployment Manager and selecting 'Update' on the Organisation but it gave the following error:
Existing SQL Server connections to the Microsoft Dynamics CRM databases
must be closed before setup can continue.
I tried the following with no success:
1. Restarted SQL Server
2. Rebooted SQL Server
3. iisreset on the Application Server
The fix was to stop the Async services and sandbox service. Then the database update went through with no problems.
UPDATE: The server needed an iisreset before the About dialog reflected the new database version.