Did you uninstall an App-V 5 client, and expected that it would cleanup after the mess it created?
Well, not all the time. After some interesting encounters – here is a small cleanup-list;
Remove the following folders;
C:\Program Files\Microsoft Application Virtualization
C:\ProgramData\App-V
C:\ProgramData\Microsoft\App-V
Remove the following registry keys;
HKLM\Software\Microsoft\AppV
Reinstall, and hopefully you are good to go!