I can't build my project on a new (git) branch with xcode 4. why?

I created a new branch of my project and now when I try to build开发者_开发技巧 and run it I get this error:

'The selected run destination is not valid for this action.' Why is this? I don't know why but I just plugged in my iphone and now the project will build. Weird.

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It can be because of:

• a missing setting, as illustrated by this blog post:

The problem was fixed regardless of the value I selected in the above list (it worked with 3.0, 4.0, 4.2 or any other value).
When I changed the value in that list though, the IPHONEOS_DEPLOYMENT_TARGET setting was added to a section in project.pbxproj and I was able to run the app on the device.

• an incorrect SDK setting. See this comment:

this is an Xcode 4 bug where it changes the platform to Mac OS X after template creation.
Close down the project, and launch it again, to fix it.