It's a sim from rc expert, Im not sure of the name but I think its called true flight the exact error message says "C:\windows\system32\autoexec.nt. The system file is not suitable for running MS-DOS and Microsoft Windows applications. Choose close to terminate the application". Like I said before I have encountered this same problem and it really wasnt a difficult fix I had to cut and paste a program in the the repair file of windows but I have forgotten how? I was told by real flight that this error has top do with windows service pack 2. I would appreciate any help out there?? I do not believe that this has anything to do with the sim im trying to load because it did the same thing to me on the oem version of real flight g2