I encountered this problem before, and had a fix that I believe involved copying files, etc. However I cannot remember how I fixed it before.
It seems to be related to saving a game when the character is in motion (moving). Upon loading the game the character reaches the destination, but then the following problems occur.
You cannot navigate freely, by holding the mouse button down. You have to click and then release, and only then will the character move.
You cannot engage enemies. CTRL key is useless as well.
Most importantly, you cannot save your game.
I tried exiting dungeons, sleeping, etc, and nothing seems to fix the problem. This is frustrating because my last usable save is an hour or two behind.
Has anyone got a fix for this problem?