Error when uninstalling Exchange 2010 from server

The other day I had to uninstall Exchange 2010 from a server with the CAS and Hub Transport roles.  It all went well until the point where it was uninstalling the Hub Transport role.  The uninstall then ground to a halt with the following error:

Log Name:      Application
Source:        MSExchange Configuration Cmdlet – Management Console
Date:          20/05/2010 4:11:01 p.m.
Event ID:      4
Task Category: General
Level:         Error
Keywords:      Classic
User:          N/A
Computer:      HUBCAS1.contoso.com
Description:
(PID 6920, Thread 31) Task Uninstall-MsiPackage writing error when processing record of index 0. Error: Microsoft.Exchange.Configuration.Tasks.TaskException: Couldn’t open package ‘D:\Program Files\Microsoft\Exchange Server\V14\Mailbox\MSFTE.MSI’. Another version of this product is already installed. Installation of this version cannot continue. To configure or remove the existing version of this product, use Add/Remove Programs on the Control Panel. Error code is 1638. —> System.ComponentModel.Win32Exception: Another version of this product is already installed. Installation of this version cannot continue. To configure or remove the existing version of this product, use Add/Remove Programs on the Control Panel
   — End of inner exception stack trace —
   at Microsoft.Exchange.Management.Deployment.MsiUtility.GetProductCode(String packagePath)
   at Microsoft.Exchange.Management.Deployment.MsiUtility.IsInstalled(String packagePath)
   at Microsoft.Exchange.Management.Deployment.UninstallMsi.InternalValidate()

After scratching my head for a few minutes, I uninstalled Update Rollup 3 for Exchange Server 2010 and then re-tried the uninstall for Exchange.  It went through perfectly. 

I hadn’t realised it was necessary to remove any Update Rollups before uninstalling Exchange, but it it seems it is required in this case.