What the installer does after running assembly installer for episerver.dll is adding performance counters for performance monitor.
So you could try to rebuild it with:
C:\WINDOWS\system32> lodctr /R
If that doesnt work you can refer to the file: PerfStringBackup.INI.
Also remember to take backup of the registry to be on the safe side.
I think you could also just remove the episerver registry keys since the manager should readd it during next install.