Hello Craig,

thank you for your help. I was able to solve the problem with an article in the internet:

"
Try to find the path for the program setup.exe in the registry.
On my machine it was c:\Programme\SAP\FrontEnd\SAPgui\FILC
\setup.exe . I do not now where it exactly was for now, but it was there...
Remove the entry. Be sure, it is the right one, search for the path-part SAP\FrontEnd\SAPgui\FILC.

Your installation unpacked it's own temporary setup.exe somwhere and tried to start it without the path information. The other installation ran, because it's path has been saved in the registry during the previous installation.
"

I found the setup.exe in the registry and deleted it.
And suddenly everything worked fine :-)

Best regards

Marcus