Did you ever get the dreaded error Error 25028.The Application Virtualization Client service could not be configured from the App-V installer? It should be effective enough to perform a manual cleanup according to the previously blog-post article by Microsoft, however there are some minor steps that eases the process in addition to what has been communicated.
A summary of steps according below;
Execute the following commands to remove the services;
sc delete sftvsa
sc delete sftlist
sc delete sftplay
sc delete sftfs
sc delete sftvol
Delete the following folders;
C:\ProgramData\Microsoft\Application Virtualization Client
c:\program files (x86)\microsoft application virtualization
%public%\documents\softgrid client
%appdata%\softgrid client
%localappdata%\softgrid client
For an App-V 4.6 SP2 client, you need to remove this registry entry;
HKEY_CLASSES_ROOT\Installer\Products\C38408D5792D40E4E9FDDD8525E15956
It may be different for an App-V 4.6 SP1 client, but you can easily find it by searching for “Virtualization”.
Reboot the client and the installation should run cleanly afterwards.
This reminds me of a related issue I had a couple of years back where I was unable to downgrade the App-V client. Or rather, it would downgrade, but then not work properly.
The .sys files for the filter drivers were being left behind (since the MSI components were marked as permanent) then not being downgraded since the MSI packages do not overwrite files if a higher version is already found on disk. So you might have to look out for and remove any of the system files also if you are looking to downgrade for any reason!