The 737NGX was working just fine for quite a while, but since yesterday I've been having two problems with it. The first is that when I load a saved flight, the plane starts wildly rotating up and down. The weirdest part is, though, that if it's far enough off the ground, it will just keep rotating but never hit the ground. It's just like when you press, I believe, F5(?) in slew mode. The second problem happens when exit a flight. The FSX window is in the bottom right-hand corner of the screen, the free flight page is blank, and it says "No Title". It's not that the program's not responding, it just isn't working properly. When I open task manager and click "end task", the "Are you sure you want to quit" window appears, I click "yes", and it quits immediately.Both of these problems started happening at the same time and only occur with the PMDG 737NGX.

Is the ngx already loaded or set as the default flight when you load the saved flight? That can cause strange issues

It was a couple times, and I wasn't sure of the exact result when it wasn't, so I just tried it. The airplane did go crazy when I loaded the flight, but FSX displayed normally when I loaded it. Can reloading the NGX corrupt the saved flight?

Loading the ngx on top of itself can cause problems. Try switching to a default plane before loading the saved flight.

Please set your default flight to the FSX default. Then load whatever you like