I've got the same problem. Everything was working fine. I've now just downloaded XCode 5, targeted iOS7, game runs but blank screen and lots of "There was an OpenGL error: 0x502" errors.
I've just installed Sparrow v2 from the master branch above as well.
Same when I target iOS 6.1 as well.
*Update*
Looking into it further, the first openGL error comes up right in the startup of Sparrow, strangely though I don't get any errors with the demo.
*Update 2*
Ok, it now seems to be working but who knows why. I selected the Sparrow project, then deployment target, which I saw was set to 5.0, changed that to 7.0 and then it worked. I even changed it back to 5.0 and it still works.
Something that is driving me up the wall though is that it keeps asking me to sign into Game Center with the simulator every time I run it, never did that before.
Also the carrier bar is at the top for some reason.