99.9% sure it's a case of Windows protecting you from yourself.
Simple solution would be to uninstall the SDKs and SBuilderX and reinstall them outside of the \Program Files(x86) folders. If it isn't too painful of an issue, include FSX as an unistall/reinstall outside of \Program Files(x86).
OK, here is what I did:
Step 1
Uninstall SBuilderX
Uninstall SDK
Step 2
Install SDK from the DVD in c:\SDK\
Install SbuilderX in c:\SBuilderX313\
Run SBuilderX
Result: Same as before
Step 3
Install SDK SP1A
Run SBuilderX
Result: Same as before
Step 4
Install SDK SP2
Run SBuilderX
Result: Same as before
Step 5
Uninstall SBuilderX
Re-install SbuilderX in c:\SBuilderX313\
Run SBuilderX
Result: Same as before
Now, as far as the uninstalling/reinstalling of FSX is concerned, I'd rather not do that. I tried it once on my previous machine (also Win7 64), and it resulted in forfeiting the ability to use it at all. It simply didn't want to reinstall - it did start initially only to inform me at the end that there was some gameinst.dll error, which, as it subsequently appeared, is quite common among the MS games, and for which there seems to be no solution (MS states there is one, but many users state otherwise, including myself, after a few days' long attempts). As reinstalling Windows, as the only remedy to return to the status quo, is not an option, I'll simply not risk it (FSX without SBuilderX is still a more attractive proposition than neither of them).
To make things even more bizarre, yesterday I installed the whole bunch on an machine with WinXP SP3 32. The locations were C:\Program Files\Microsoft Games\Microsoft Flight Simulator X, C:\Program Files\Microsoft Games\Microsoft Flight Simulator X SDK, and C:\Program Files\SBuildrX313.
The results were exactly the same as on Win7 64.
If this helps, the FSX I use is FSX Deluxe with SP2 (no Acceleration).