I would expect the NSV is closing its connection after the first VI runs. Try making a third "master" VI with a button for "run VI 1" and "run VI 2". Run 1 first, then try 2. If you just run 1 once, it'll open the connection to the NSV, but after it closes there won't be any VI's accessing the NSV, so it'll probably auto-release the reference.
You need to make sure the reference remains in memory, otherwise it'll probably get auto-closed.