Self casting not working with Mouse 4 button

So since i have been playing LoL with smart casting have have used my M4 button as my self cast for some of my mains: Morg, Karma, and Nami.. all their E abilities... now the ALT+E does work.. but until recently my mouse button 4 binding isnt even recognized.. i try and rebind it and the client doesnt even let me choose M4B as a key to bind it to.. anyone else having this issue???