Can you close a warp point that is connected to a system with a system gravitional shield? So, one point is in a protected system, the other is in a non-protected system...
No you can't. If the system on either one side or the other of the warp point has a system shield, then warp point openers/closer fail on that warp point.
Now if there's an empty system between -- sure, that works. Watch out for interesting activity in nebula and asteroid systems...