It's a known stock SHIII bug related to ending a patrol with renown lower than a threshold I can't recall off the top of my head. Otherwise it can be caused if you try to load an old pre-GWX career when you start using GWX.
Read here:
http://www.subsim.com/radioroom/showthread.php?t=122897 and here:
http://www.subsim.com/radioroom/showthread.php?t=119156 for the workaround.