I was having the same problem even with SDK 4.0 installed, then I remembered that I also installed the developer preview of Xcode 4.
Turns out that installing Xcode 4 will select Xcode 4/iOS 4.1 as the default SDK, even if 4.0 is still installed. But there is an easy fix that doesn’t require reinstall Xcode.
Run “/usr/bin/xcode-select -print-path” and check the path. I was getting /Xcode4 that is where the preview gets installed to not interfere with the standard version of Xcode in /Developer.
Run “/usr/bin/xcode-select -switch /Developer” to select the original version of Xcode and iOS SDK 4.0.
After that I can run Corona and don’t get the error message anymore.
[import]uid: 456 topic_id: 1884 reply_id: 5683[/import]