Exchange Unified Messaging Speech Service will not start.. Event 26191

During my deployment of Exchange 2007 SP2 and also in the past when attempting to install the unified messaging role on server 2008, I encountered an issue
in that the UM services would not start. In event viewer, you will be presented with the following error in the application log.

Event Source: Microsoft Exchange Speech Engine
Event ID: 26191

Description: The main service was unable to start. Please check that it is configured correctly. Details: ‘Invalid class ‘.

Fun! After scouring the internet again for a resolution to this error and not finding anything I started to dig into the service and dependencies. The speech engine
service relies on both the RPC and WMI services to be running to start successfully. I check both and they were in fact running. After taking a step back to think
about the requirements for Exchange and many other Microsoft products I landed on the .Net Framework. Then it clicked, DISABLE ROLLBACK.

Without realizing, I made two changes at the same time so I am not sure which resolved the issue but, after changing the disable rollback registry setting and disabling
antivirus on the server, I was able to successfully run the SP2 install and start both services. The disable rollback registry key is located at,



Modify the setting from a 1 to a 0 and rerun setup. I can only assume that this was my problem as I did NOT have to unload antivirus on any other server role that was
upgraded to Exchange 2007 SP2. Hopefully this will help a frustrated Exchange admin…


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