Unable to build: the file dx.jar was not loaded from the SDK folder 错误
platform-tools\lib folder was missing after upgrade (my eclipse was open). close eclipse, using sdk manager uninstall and install "Android SDK platform-tools".即先关闭eclipse，打开sdk安装目录下的SDK Manager.exe 顶部Tools 下面的两个勾选上以后点击下面的 Install packages 按钮更新，更新完成后启动eclipse就可以了
注：后来在另外一台电脑发现，如果sdk没有更新到最新版Tools下面的两个包是安装不了的，所以必须先更新sdk然后再更新Tools才行。
