1、从网上下载一个程序，在编译时出现下面的错误：
The run destination My Mac 64-bit is not valid for Running the scheme 'MyTest'.
The scheme 'MyTest' contains no buildables that can be built for the SDKs supported by the run destination My Mac 64-bit. Make sure your targets all specify SDKs that are supported by this version of Xcode.
解决方法是：在Build Setting中，将Base SDK,全部修改成iOS 5.1
如下图所示：
