Well, basically you can only edit qvw files which are accessed on the QV Desktop as well as they are local files.
i.e. you can not access files through QV Server and be able to edit them. You should have access to QVW file directly.
QVW files accessed through servers are read only they can not be written back. Even the objects users create though web access they are saved separately into [Name].qvw.shared file and not into the QVW file directly.