Did you try to build your project in XCode 4 for the first time and get an error that starts with “There is no SDK with the name or path”?

That happened to me recently.  And the path given in the message had nothing to do with SDK’s.  In fact it was an open-source sub-project I was using.

I Googled for the answer, but mostly just found references to posts on how to fix actual SDK path problems.

It turned out that the problem was how XCode 4 looked at the sub-project.  Somehow, XCode 4 had noticed a missing Base SDK, had a static library as the product, and assumed it was a Mac OS X project.

I closed the project and opened the sub-project directly.  I corrected the project settings back to iOS and it built correctly. Closing and going back to the first project, the build now built correctly (with some warnings that I did not recall from XCode 3.)