Apparently when you change the clock on your computer while in-game, the available EP displayed increases based on what you should have at the new time.  This only works going forward, not backward.

Set your clock an hour ahead?  60 more EP.  An hour back?  No change.

Of course, the game server knows you don't have enough EP so you can't spend it, but can still be confusing when your available EP jumps up out of nowhere.