This is a rare bug that usually happens when all chat tabs are disabled. Do the following steps to fix the problem:
1) Navigate to the folder: C:\Users\your windows username\AppData\Local\dof\
Keep in mind you might have to set "Show Hidden Files" On in the Tools - Folder Options (it's at the top bar on any window explorer window)
2) Inside that \dof\ folder you'll find a file called local_saved_data, delete that file, and restart the game.