I unchecked the compatibility settings and its working now.
That's what I've said in one of my previous posts:
The compatibility mode shouldn't be touched, meaning it needs to stay without any of the compatibility modes enabled
This is valid for both FSX and the Couatl exe. I really can't see why one would suggest to use a compatibility mode to make the sim running better. What compatibility mode does, is to re-route file read/write into folders that a Vista/7 user can write to, for older program that do not take into accout non-writable folders in Vista/7, like C:\Program Files, C:\Windows, etc. so, if anything, the program should run slower, not faster, since every file access is re-routed...
In any case, FSX is fully Vista-compliant so, there's no need to enable any of the compatibility modes. The only Vista/7 feature that FSX doesn't support, is Aero but, it's automatically disabled anyway, when FSX starts.