In App-V 5.0 if you see the above issue,try to reinitialize the wmi namespace. This can be done by using the below command in an elevated CMD.

mofcomp "C:\Program Files\Microsoft Application Virtualization\Client\AppvClientWmiProvider\Microsoft.Appv.AppvClientWmi.mof"

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For alternative solutions check my blog page - http://app2pack.blogspot.com/2015/11/failed-to-open-wmi-namespace.html