I accidentally clicked on the 'Build New Base' tab and everything (fast forward, bases, research, xenopedia etc) became locked out. I was still able to interact with the geoscape and get to the base screen by clicking on my base, send out interceptors, etc. I think I may have been locked into the 'Build New Base' cursor. It was fairly early game, I had been on maybe two crashed UFO missions. I was researching early stuff, Alien Invasion and Caesan Autopsy. Quitting to the main menu and reloading fixed it.
EDIT:
This happened again, it seems that I just needed to right-click to cancel the build base cursor.