Thats weird. I ran into the same problem (not being able to add), then realized you had to run the installer. But it didnt re-arrange my icons.I have the iPhone version and it does me no good, it still won't add. But then I do the fix off the Installer app and then it is all good, but my icons are all re-arranged, as it said in the warning. But... then I go to re-arrange my icons back to normal and when I do, guess what doesn't work.. the add function, it's a freakin' see saw and it's driving me insane.
When I jailbroke the first time, it was good and well, but for some reason, no go now... All my other iphone apps work!