Well until I get a full thread up here with the same information let me copy and paste the reddit thread into here. I would suggest using the beta build of the NoX SDL project Zoa and I are putting some time into. The reason you are getting that error is that when you are alt tabbing NoX is losing its lock on the surface and it is getting corrupted, with the SDL project that won't be an issue, as well as you can run it in borderless windowed mode which means alt tabbing will be painless.
Thread:
http://www.reddit.com/r/Nox/comments/1aa6nf/nox_sdl_insertion/Direct link to download:
File Download:
http://www.noxhub.net/Downloads/NoXloader.zipIt comes in a zip file that just needs its contents to be dropped into your NoX installation directory and then you just run runnox.bat. It uses microsofts Detours library to inject the .DLL into nox and run our code. It ships with a noxSDL.cfg file to configure the new settings, I'm packaging a readme-NoxSDL.txt file with it now to explain using the cfg file.
Original thread on this forum (messy and not concise):
Forum Thread:
http://www.noxforum.net/index.php?topic=8677.0The current largest problem is acceleration not working with both renderers (opengl and directx) on every card so you have to change renderers in the config file or (heaven forbid) run it without acceleration (really ugly resizing).