be aware that the cmd will be executed on the Qlikview server.
This is the C drive of the Qlikview server, not your local one.
Also like Diego mentioned, try to execute the command directly on the Qlikview Server as the user under the Qlikview service run. (Take a look at the services).
And maybe a DEL /F is necessary if the myApp.qvw file is read-only.
Try DEL /? for further help.
Hope this helps,