Can't Move In First "Crossing Lines" mission

Howdy...need some help.

Finished the Crossing Lines episode and went on to play the other single player missions.

I now want to go back and collect all the letters. So, I'm starting the Crossing Lines mission again in easy mode. I get to the first part where Mason gives me the binoculars to scope out the German air base. That works fine. But, once I put the binoculars away, I can't move at all other than jump up and down. I tried remapping the keys and that didn't work. I then reset the key mapping to factory standard. W-A-S-D should move me around but the keys simply don't do anything! Thus I'm stuck with Mason and can't continue the mission to find the letters.

As I said previously, the first time or two that I've played this specific mission, I was able to move just fine and completed it.

Help!

Thanks

Tim