The is a key compbination that allows you to open the Origin interface without Alt-tabbing out of the game. This is called the overlay-it overlays itself on top of the game.
It can be turned off in Orgin's options, which is probably what you did without understanding what it was. The overlay was causing some problems before the first major patch, so perhaps you disabled it as some people were suggesting.
At any rate, make sure that is turned on in the options. If it is enabled, then disable it, save and quit Origin, the restart Origin and enable it. If you still get the error then you will have to dig through the EA Answers knowledgebase about what could be causing problems with the overlay.