So i suddenly had the problem myself recently (started after patch 5), I would start up the game and it would show the loading screen and when it was almost done the game would simply shut down.
It didnt help to reinstall the game, del all things in registry that had "starcraft" in it so i got quite sad
So! i searched the webz and i found my answer! This fixed my problem and it might fix your problem aswell
Remember to enable "show hidden files, folders, or drives: HOWTO: http://forums.majorgeeks.com/showthread.php?t=74220
Windows 7/Visa: Go in to C:\Users\YOUR USER NAME\AppData\Local\Blizzard Entertainment
Windows XP: C:\Documents and Settings\YOUR USER NAME\Local Settings\Application Data\Blizzard Entertainment\
And simply DELETE the Battle.net folder, this should fix your problem as starcraft 2 now will make a new of these folders the next time you open starcraft 2
Hope this helps you!!
PS: KEEP UP THE GOOD WORK SC2 CRACKER COMMUNITY
(edit: Added the path for xp users (thank you apriores)