Hi!Some days ago I upgraded my Windows XP Pro where FS9 runs on to SP1a. Now I am no longer able to load the 737 into FS9. Each time I select the 737 (no matter if 600, 700, 800 or 900), FS9 shows up an error message and identifies the main gauge file of the 737 as the process that caused the error and asks if I want to restart FS9 or send the error report to Microsoft. I did not install any addons in the last few weeks and I also did not change any configuration settings of FS9 or my PC. The only thing I changed was installing the service pack for Windows. Before that, the 737NG worked without any problems. Any advice on this?yours,Thorsten

Try using the PMDG removal tool (available on PMDG web site) and then re-install the NG.

And use the opportunity to update XP to the latest service level as well (SP2 + hotfixes).