摘要：
升级adt插件后，eclipse突然出现Unable to build: the file dx.jar was not loaded from the SDK folder 错误
Unknown error: Unable to build: the file dx.jar was not loaded from the SDK folder!
升级adt插件后，eclipse突然出现上面错误，无法运行android项目。
网上搜索了很多方法试过了都不行，clean，换workspace目录，把tools下的dx.jar拷贝到对应platform下面也不行，重启eclipse，更新sdk都不行。
最终在stackoverflow上搜索到一个方法试了以后才可以
platform-tools\lib folder was missing after upgrade (my eclipse was open). close eclipse, using sdk manager uninstall and install "Android SDK platform-tools". 阅读全文