I think I've seen other people have this problem before and I've tried deleting the pref.prop file and also checking compatibility mode for Steam and the game itself. I can't seem to figure out what's causing it. I played through the first 5 episodes earlier this year with no problem and ever since I've installed the 400 Days of Summer add-on I've had this issue.
CPU - i7 3770k GPU - GTX 680 x 2 MOBO - MSI Z77 UD65 RAM - 8 GB Vengeance OS - Windows 7 Ultimate
Here is the link for the TWD Support Data: http://www.sendspace.com/file/p2w38k
I've seen it mentioned before and I don't know if it could be a problem but I am using my PS3 as a gamepad. I'm not using Motionjoy but rather BetterDS3.