I had the same problem, thank god I found this post.
A quite silly move, I installed the sceneries whilst FS was on, restarted the program then it just quit on the splash-screen. I uninstalled both LSGG and KLAS, tried again to start FS, still no luck.
Anyways, I tried resinstalling them again, this time with FS turned off. After installing them both, I tried FS and it worked.
That's another method I guess.