One last possible solution.
I had successfully installed the 737,then problems started happening. I deleted the 737 everywhere a trace of it could be found, cleaned out the registry of CS 737 entries, tried reinstalling running as admin, antivirus and firewalls off, but the plane was dead after I reinstalled it. I tried everything I could think of in my research. Nothing worked.
I had to do a entire FSX reinstall anyway and when i did, everything reinstalled perfectly on the fresh FSX/Acceleration except the 737. Finally, I downloaded the installer on Explorer rather than Mozilla and it worked. So try using Explorer if you haven't already.