Groping in the dark...
Maybe this issue has something to do with a graphic card change (NVidia to ATI)? Finally, I found that it was the point I was not able to launch FSX from, without that error.
I'm not much confident about finding a solution, but, let me tell you the whole story, just in case it helps.
1. Sometimes my computer did not start.
2. I detected some boot disk problems (or I thought so).
3. I tried to enter Windows safe mode.
4. Some time ago I changed my graphics card to a GTX 560. I read that my computer does not support windows safe mode, unless it has the original graphics card plugged. I change it.
5. Finally, Windows started in safe mode. But it remained busy for a long time before it started, just like if it was doing some windows update (no more information on screen).
6. Disk checked, found errors, everything resolved. Back to my GTX graphics card, and to Windows normal mode.
7. Windows started with no delay (I guess that NVidia drivers were present, and there was no need to re-install it).
8. Error arised when starting FSX for the first time, after all this mess. Previously I enjoyed LHBP scenery a lot.
9. Meanwhile I found out that the problem was caused by my pc power supply unit. Now, changed.
At present time, FSX is not able now to start, maybe those p.s.u. failures have corrupted some configuration files. Trying to reinstall. But as I have told you in another topic, my registration code is now banned, maybe due to many reactivation tries. Now waiting for a solution.