Uninstall 800xA correctly
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There exist no golden procedure appropriate for all possible permutations of System 800xA and third party software options (Oracle, SQL Server, RTDB, etc).
Suggest restoring a drive image backup taken before installing System 800xA.
Murphy's First and Second Law of Computers are still very applicable:
1) Backup often
2) Backup early
This is uncharted territory, but:
1) Stop system
2) Delete system
3) Use AfwKill to stop all ABB running services. Could be that the Installer Agent still is running, kill it as well.
4) Use Add/Remove program to uninstall 800xA related SW
5) Delete the "C:\ProgramData\ABB" folder
6) Remove ABB prefix related Enviroment Variables for the service and installer User.
It worked for me...