Check the cave item fpe file for the forcesimpleobstacle = 3 statement.
Also the cave sections that came with the DLC stuff, The floor was to thick to have AI walk on it. Have not tried them after the AI upgrade to see if they do work now.
Which cave pieces are you using for your stuff?
You can also press (tab tab) while in test game and turn on the debug mode to over 10 and the collision lines should show. Check to see if one of the boundaries is stopping your character from moving.
Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz, 2400 Mhz, 4 Core(s), 4 Logical Processor(s), 8gb RAM, Nvidia gtx660, Windows 7 Pro 64bit, Screen resolution 1680 x 1050.