The Addon Manager for FS9 works without any problems in Windows 7. The most likely cause of a crash is your antivirus, that is either blocking or trying to "heal" it, thus corrupting it.
As explained in many other thread, you have to:
- Download and install with the antivirus entirely turned OFF
- BEFORE turning it back on, configure it to exclude the following file from scanning:
YourFS9Folder\MODULES\bglman.dll
Only then you can turn the antivirus back on and launch FS9.
And, be sure your Windows is fully updated, even with all optional downloads and hotfixes.