问题描述：
帮客户的iPad安装AD demo，机器SDK是4.2.1，客户iPad SDK是3.2，直接developer debug不成功。
问题分析：
把“Project Settings”的"Build"选项卡里的"Base SDK"设置为"Latest iOS"（最高），并把"iOS Deployment Target"设置为"iOS 3.0"（最低）。
问题解决：
网上查了下，看到一老外的解决办法，如下：
I believe the only requirement is that you edit and resave the info.plist file. I editted to 1.7, saved, and then back to 1.0 and it worked fine.
It may be that XCode is binding in additional details from the build settings at the time of packaging and since the info.plist hadn't changed those additional bindings did not get attached. If this is the case I would consider it a bug.
我也认为是一个iOS的Bug，只有修改info.plist才会导致project settings设置生效。