I had this issue but the solution didn't work for me. It actually turned out to be a permissions issue.
The suggested solution worked, but you probably had two issues at the same time, so you also had to fix your permission, but this shouldn't have anything to do with any of our products, that never try to write into the FSX folder when running (they only write into %APPDATA% or %PROGRAMDATA%, so they shouldn't affected by permissions in the FSX root folder).
I still have an issue though with FSX crashing to desktop after I finish a flight and am exiting FSX...thoughts? I am running Active Sky Next, EZDok, GSX and VPilot along side the boxed edition of FSX, PMDG 777 and 737.
That seems to be another, unrelated, problem. Try to disable all the other products (except FSDT's), and re-enable all of them, one by one, until you find the cause.
In any case, I can only confirm that, in relationship to the startup crash, this IS fixed by reinstalling the Stand-Alone Addon Manager now.
Let's try not to morph this thread into a general discussion of any non-FSDT related FSX crash, which will only make this very confusing and impossible to follow.