The embedded Lotus Notes viewer was not working on some customer workstations although all necessary files were correctly installed and the KEYVIEW.INI had the correct Notes program path configured.
After some investigation we found out that a German Notes client installation does have a second KEYVIEW.INI besides the one in the Notes directory. It is stored in ..\NOTES\MUI\DE\ and must also have the correct path of the Notes program directory configured. After we corrected the path name the viewers were ok again.
I was not aware of this speciality of the German client (I suppose the same is true for other languages than English).