The Power Manager just displayed an empty list of power schemes and saving a new one did not add it to the list, the new one just disappeared after saving.
Removing the software and reinstalling after a reboot did not fix the problem so I had to check the Windows Registry and found that the application had added a huge amount of power policies for unknown reason. I guess the application has problems with too many policies (overflow situation) and that causes the error message.
I deleted most of the power policies and restarted my Thinkpad.
This fixed the problem, I can now use the Thinkpad Power Manager again.
I still recommend to use Thinkpads, especially the Txx Series.