Default [Q] My android phone all of a sudden stopped letting me drag and drop files onto it

I am running a CM11 Nightly on my jfltevzw. I am trying to update to a new nightly by dragging and dropping it onto my phone, the way I always do. However for some reason when I try to do it now, I get an error message saying "Cannot copy item: This device has either stopped responding or has been disconnected." even though it shows up on my explorer. I have no idea what happened. It was working fine like a day ago. I have rebooted my computer and everything, but it just won't work. Help!