FSX ATC and cruising altitude problem

Hello everyone!

I've been having a intermittent problem with the ATC on FSX:SE for a little while now.

After creating a IFR flight plan (either in FSX or Plan-G) and entering a cruise FL (say FL320), the ATC will ask me to climb above that when I reach my desired altitude, usually more than 10,000!

I've checked the flight plan XML and everything seems fine with the cruise altitude, and there doesn't seem to be a pattern such as a/c or specific routes.

When I cancel the IFR clearance and try and load the flight again through the planner, FSX usually freezes and crashes to the desktop.

I remember having the exact same problem with the boxed FSX Acceleration a few years back without finding out what caused it.

I'd appreciate any help on this matter since I rarely have the time to fly nowadays and the stock ATC is basically my only option.

Thanks!

My setup is as follows:

Win10 Pro English

FSX:SE

Rex Skyforce 3D

AS2016

Pilots NG Mesh

Orbx Global, FTX Vector, LC Europe