Lightroom Classic CC 8.1 Panorama erstellen nicht möglich

There is no difference. In the meantime I uninstalled und reinstalled the application, I think 3 or more times. I followed the instruction of a Adobe support assistant to clean up the entire PC from ALL Adobe applications, delete all Adobe directories and all Adobe entries in the Registry. The new clean installation works quite well with some restrictions. It is still impossible to select simply any pictures which could/should be merged. For instance I selected 4 pictures that should be merged, Lightroom says that these can't be combined. But when I take the first and the second one, these can be merged easily, the same happens when I take the third and fourth picture. And surprisingly I can combine the both panoramas (1+2) and (3+4) to the disired panorama consisting the origin 4 pictures. I still do not understand what criterias Lightroom takes to decide wether it is possible or not to merge pictures.