How to delete unselectable faces? I'm trying to model a little pistol for my game and I ran into this problem:

I was connecting my vertices and an unselectable face showed up. I would like to remove this face but it isn't selectable :( 

I have ran into this problems multiple times. What I did before was deleting all the vertices around this face. Then I would have to remake and reconnect all the vertices again which lead to a lot of work. Is there a better way?
The face is probably a lot bigger than what you think, my guess would be that it cover the whole top surface, not just the white bit you see overlapping. In edit mode, face selection, X-ray ON,  you might be able to see the center of the face and select it. If you really can't, then you'll have to fix it manually.