Well, at last, I solved the problem with your help DavidR.
Here it is:
I originally installed Avast and afterwards when reinstalled Avast, every time in the C:\Program Files\Alwil Software\Avast4 directory which was always the default. Then later you asked me to look in the registry in the "PendingFileRenameOperations" and post it's contents. At that time I didn't notice that it was showing \??\D:\PROGRA~2\ALWILS~1\Avast4\Setup\reboot.txt and all the other files also showed the D: drive which should have raised a flag to me showing D:\PROGRA~2.
I looked at this again last night and it hit me. I have an unusual setup. Because I have a small C: drive so that it's easy to backup I created a Junction Link for the C:\Program Files. In this way the files are located in the D:\Program FilesC directory but also appear in the C:\Program Files directory. I have about 4.7.Gb of program files in the Program FilesC directory on the D: drive mirrored onto the C: drive as Program Files. All programs have worked up till now except Avast. With that registry key showing the D: drive, obviously Avast has found a duplicate installation or considered it a conflict.
I uninstalled Avast again and reinstalled it into D:\Program Files (not D:\Program FilesC). Did a manual update of the program from 1169 to 1201. The virus database updated automatically. I had to reboot after the program update. It's up to date now and working. Now there is no reboot.txt file present and there is no "PendingFileRenameOperations" key in the registry.
Thanks a lot again.
Frank1