Updated to Xcode version 4.2 iOS5 and started see this error for all my projects.
The project builds however when trying to submit to appstore, the validation fails and generates this warning and error: warning: iPhone apps should include an armv6 architecture (current ARCHS = "armv7")
iPhone/iPod Touch: application executable is missing a required architecture. At least one of the following architecture(s) must be present: armv6 (-19033)
Architectures is: Standard
Base SDK: Latest iOS (currently set to iOS 4.2)
Valid Architectures: armv6 armv7
Most likely the architecture are not defined in the project. It should be Architectures is: Standard (armv6 armv7)
Also make sure this is the case for the Distribution profile in this case. If needed delete the existing values and add it again. Then build and try.