windows 7 or 8? if u use win 8 try the tool RadeonPro(also work with nvidia cards)....if u use win7 try out the Configurator with SweetFX 1.5.1(http://sweetfx.thelazy.net/)...Configurator works fine for me :)
Just download my "all required files" and Unzip "Squall - The evil within SweetFX.rar" into the Assassin's Creed Black Flag IV main game folder. The game and sweetfx should be work now. If you don't like the preset change Sweetfx_Settings file whatever you like.
Link is here: http://sfx.thelazy.net/games/preset/2300/
You can also try SFXConfig from here, if you do be sure to let me know how it worked for you!
http://sfx.thelazy.net/forum/sweetfx/44/
Get v1.4 at the bottom of the thread...