Ehm, don't ever modify permissions of system folders (Program Files, Users, Windows, etc)... You'll only make your system vulnerable/unstable. Either install the program you have problems with to another non-system drive, or change permissions only on a file-by-file or folder-by-folder bases where required, but not the entire parent folders
Games should never be installed to Program Files or even a system drive anyway.
In your case, only the MODS folder would do...