Can't Upgrade or Uninstall VM Pro 1

[Nortel4Ever]

I was trying to do an upgrade of VM Pro 8.1 to 10 then 11.0.4.4 on a Windows 2008 Server. The upgrade would not run as a file called IP Office Voicemail Pro.msi was missing from the 8.1 install folder. I can find this file in the install folders of VM 9 10 and 11. Is it as easy as just copying this file into the 8.1 install folder or do I need to get one from a 8.1 install folder somewhere else?
I also tried uninstalling VM Pro using Add Remove Programs but received an error saying the program could not me uninstalled.

 

[TouchToneTommy]

Download a fresh copy of Voicemail Pro 8.1, run a repair install, then run it again to un-install?

OR, leave it installed and upgrade it to 9.0, then 9.1, 10, 10.1, and finally 11 ?

 

[Nortel4Ever]

The oldest version of VM Pro 8.1 I can find on Avaya's support site is 8.1.9203, but the version currently installed is 8.1.1096. Would I be okay with doing a repair with the .9203 version?