I've got the same problem, not sure what to do.
Anyone know what's going on?
EDIT: Played single player for awhile until i got booted out by a Impulse alert that the update was available. It took awhile, but it's downloading now. If it hasn't hit you yet, don't worry, it's coming! 
NOTE: I just noticed this now, but if you rightclick the system tray icon for impulse, you can change settings, one of which is for "check for application updates." Mine was set to 180 minutes, so maybe it didn't bother check for about 3 hours. Try lowering the time, we'll see if it'll help by making the application check for the update (not sure). Let me know if that works for anyone!