When upgrading a CRM 3.0 implementation using host headers, a tricky little bug may occur that is very difficult to diagnose. The bug exists within the actual installation package of CRM 4.0, where the installation will use the machine name of the CRM server instead of the host header name. So the former address of http://<hostheader>/ will now be replaced with http://<servername>/, which of course doesn't exist.. What is more interesting, and what causes this to be hard to troubleshoot, is that when this happens the web UI will operate just as it should after the upgrade. You will be able to type in http://<hostheader>/ and it will direct you to your upgraded 4.0 implementation. Where CRM will "break" is when you attempt to run workflow's or configure the Outlook client. At this point, it will throw an error that states that the CRM server cannot be reached, and that it may be down.
The fix for this is very straightforward, although unsupported since it requires direct updates to the MSCRM_CONFIG database. Simply open up the DeploymentProperties table within this database and change the entries for AsyncSdkRootDomain, ADSdkRootDomain and ADWebApplicationRootDomain to reference your host header. Or, if you don't like making manual modifications to your database, you can run this script:
USE MSCRM_CONFIG
DECLARE @HostHdr VARCHAR(250)
SET @HostHdr = 'hostheader'
Update DeploymentProperties SET NVarCharColumn = @HostHdr WHERE ColumnName = 'AsyncSdkRootDomain'
Update DeploymentProperties SET NvarCharColumn = @HostHdr WHERE ColumnName = 'ADSdkRootDomain'
Update DeploymentProperties SET NvarCharColumn = @HostHdr WHERE ColumnName = 'ADWebApplicationRootDomain'
GO
Just change the value of the @HostHdr variable to whatever you need it to be, and run the script.
After that, all you need to do is run an IISReset, and restart the CRM Async service and you will be good to go. As a friendly reminder, this is unsupported and should be considered informational only.
