I have massive problems with my developed software and the latest Flash Version (Version 126.96.36.199) for Mac. So I need urgent a download link for the flash release before that. Thank you!
Previous versions of Flash Player are posted at Archived Flash Player versions. You'll first need to uninstall the latest version using the uninstaller posted at Uninstall Flash Player | Windows and then you can install the previous version.
For the issues you're encountering with your software, please file a bug at http://bugbase.adobe.com/. Please see the tech note Report a Flash Player crash for more information on filing a bug and what information to provide. If you can, adding source code/simple swf exhibiting the problem will be very helpful.
If you need to downgrade, I suggest that you get the latest ESR release 188.8.131.529 from Maria's archive link.