I've finally been able to complete the tutorial flight (three times in a row) with no freezes or CTDs. Before today I have never even got half-way to Schiphol before the simulator crashed. The cause of my problems was, suprisingly, having my controllers connected via a USB hub. I had a CH yoke, CH throttle quadrant, Sidewinder steering wheel (which I actually use as rudder :) and a mouse all connected through a four port USB hub. After a gazillion reinstalls and config changes I decided to remove all controls and try with the yoke only. Suddenly all stability issues were gone! I've now added the steering wheel and the throttle quadrant, but skipped the hub itself and it still runs perfectly. The sim has worked smoothly using the USB hub when flying the default planes, the F1 cessna citation mustang, and a number of other addon planes, but failed completely with the PMDG 737 NGX. So if your NGX keeps freezing, you might want to try to connect your controllers directly to the computer and it just might solve the problem. This is my second attempt at posting this, I have to assume that the first was removed by the moderators. I can't see that it breaks any forum rules, but please notify me if there is a problem with it.