Default [Q] Accidentally Deleted Multi-Window

Hi everyone,

I just got my new AT&T Galaxy S4 (32GB) and in my zealousness to delete everything that came preinstalled that I felt I didn't want, I must have accidentally deleted whatever makes multi-window work on this phone. I'm using Titanium Backup to delete the apps. I have multi-window enabled but when I long-press the back button nothing happens except for the slight vibration telling you multi-window was activated successfully. I never see the white tab on the left hand side of my screen. I've tried a few third-party multi-window managers but I get the same results with any one I try.

Can someone please help me get multi-window back?

Thanks!