你改名解压目录？如果是，不这样做。或者，如果你改变解压目录的位置有可能发生。

Did you renamed the unzipped directory? If yes, don't do this. Or it may happen if you changed the location of unzipped directory.

解决方案（如果你不想再解压缩ADT束）

Solution (If you don't want to unzip ADT bundle again)

在Eclipse中： - 转到窗口 - ＆GT; preferences-＆GT;的Andr​​oid ，你会看到 SDK位置。
浏览到您的SDK位置，并说确定。

In Eclipse:- goto Window->Preferences->Android and you will see "SDK Location". Browse to your SDK location and say OK.