I just spent an hour tracking down this error, I was trying to deploy to my iPhone device after testing in the simulator, and upgrading to a universal application. I found that I was unable to select armv6 from the active architecture window. I kept getting the error:
I selected project settings from xcode, and everything was set up. What I finally figured out is that I had to select the target, and then select 'Get Info' in order to display the dialog for MY TARGET. From there I found my Architectures was set incorrectly. I changed it to standard, (armv6 & armv7) and then I was able to deploy to my target device.
The key concept to remember seems to be that the targets is what matters, not the project setting (which is different from Visual Studio).