Reason was that my Win32 library path has gone corrupt through some circumstances (I remember of some GetIt Packages which I have installed, and some, which I have deinstalled). Thank's to Bruno Fierens for the hints.
Because I had no backup of these settings I decided to uninstall and install C++ Builder 11.1 again.
That worked! Now a can install TMS Packages like I have done in the past.
Thank's a lot.
Andreas