Are your characters crouched over and the screen darker than normal? I think maybe during that battle you accidentally switched to sneak mode. Check that your lead character's secondary skill is set to sneak (using the icon by the character's portrait), and then right click on the ground somewhere to return to normal.
A couple people have switched to sneak mode without realizing it, and posted in the forum about no longer being able to run and/or the screen being dark.
