解决问题:The run destination My Mac 64-bit is not valid for Running the scheme

转自：http://www.cocoachina.com/bbs/read.php?tid=78319

How to change the SDK:

1) Click on the project icon in the left hand panel.

2) In the right hand panel that appears, select Build Settings » all.

3) You'll see the option to change the SDK. Screenshot

4) 修改Base SDK。