Have apple introduced the iPhone 3GS they made an major switch in processor architecture, the want from armv6 to armv7.
Now that we have all update to Xcode 4 with iOS 5, Apple seems to be of the opinion that you can drop support of the armv6 architecture.
Well this isn’t always the case, especial for those device that can run iOS 4.*.
Luckily you solve this very easily, go to the the project build setting.
Here you will see that the “Architectures” is set to armv7, which is de new default architecture.
When you select the Architectures you can select an architecture from the list. Here you want to select “Other”.
You will be presented with this edit view, remove the existing value.
Then add “armv6″ and “armv7″ to make your app compatibel with the old device.
And you’r done, connect one of the armv6 device and keep you fingers crossed that you app runs with out any error.
UPDATE
The latest version of Xcode will also add “armv7″ to the Required device capabilities in your info.plist.
Just remove it from there.