Please check out the system administrator's guide, here:
https://www.adobe.com/devnet/flashplayer/articles/flash_player_admin_guide.html
Common problems typically fall into the buckets of:
- mms.cfg is installed in the wrong place
- the wrong directives are specified
- mms.cfg is saved in a weird encoding (i.e. we're not going to parse the config file if you saved it in UTF-7... it's happened...)
If none of that helps, can you provide a copy of your mms.cfg and a clear description of where you're installing it, etc. Also, does Flash Player running as the user have permission to read the file? If you deployed it with permissions that don't allow it to be read at runtime, that would not work well.