Sometimes when opening the "SDK manager", a error may violate:
The error state: failed to execute tools\android.bat : The system cannot find the file specified.
The solution is easy:
Extract the android-sdk-windows\temp\tools_r??-windows.zip (?? means the version number, if there are several versions, select the max one!) to the android-sdk-windows folder.
Note the above steps is to replace the bad android-sdk-windows\tools folder with a good one.
Note if the folder name is not "tools", rename it to "tools".
Note: the solution is from zhidao.baidu.com. original from: ljqiandu6