After installing the above update for AVR8 and ARM processors (without ASF) it was no longer possible to load an existing project. The error message was (appeared in German, the installed Win10 language, here translated:
C:\Users\Jerry\Dropbox\SAMD21VTI\SAMD21VTI\SAMD21VTI.cproj : error : The file or Assembly "Fdk.Project, Version=188.8.131.52, Culture=neutral, PublicKeyToken=202c1f4821a358a9" or a dependence of this was not found. The system cannot find the file
It couldn't even output Help->About Atmel Studio. An error box appeared "Could not find a part of the path 'C:\PROGRAM FILES (X86)\ATMEL\STUDIO\7.0\EXTENSIONS\ATMEL\ACME-STUDIO\7.0.102\extension.manifest'
The system runs 64-bit Win 10, German.