If you are getting "The Application Virtulisation Client could not be started" error and it will not allow to start App-V client service if you try manually. Also if you to to uninstall and install App-v client the result is same.
The above issue is because your WMI is corrupt to resolve this issue you need to repair WMI repository, to repair WMI you need to use following bat script
@echo off
pushd c:\windows\system32\wbem
sc pause winmgmt
for /f %%1 in ('dir /b *reposit*.') do rd /s /q %%1
sc continue winmgmt
pushd "c:\program files\citrix\system32\citrix\wmi"
for /f %%1 in ('dir /b *.mof') do mofcomp %%1
pushd c:\windows\system32
regsvr32 /s scecli.dll
regsvr32 /s userenv.dll
regsvr32 /s /n /I userenv.dll
pushd c:\windows\system32\wbem
for /f %%1 in ('dir /b *.dll') do regsvr32 /s %%1
for /f %%1 in ('dir /b *.mof') do mofcomp %%1
for /f %%1 in ('dir /b *.mfl') do mofcomp %%1
popd
popd
popd
popd
