Just updated to iOS 6 sdk and latest Xcode and get this when trying to build to my 3gs. I 've added armv6 under valid architectures?
"Could not change executable permissions on the application"
I could solve it erasing an application that I had previously uploaded using the same Bundle Identifier (xcode get's confused doing the chmod). Try checking the log from xCode Organizer (Your device's Name -> Console) you should get information from that log. Good luck!