Ionic run android faild

Ionic -V 1.2.13
cordova -v 4.1.2

BUILD FAILED
G:\ionic\install\ionicAndroidPlatforms\sdk\tools\ant\build.xml:932: The followin
g error occurred while executing this line:
G:\ionic\install\ionicAndroidPlatforms\sdk\tools\ant\build.xml:950: null returne
d: 1

Total time: 59 seconds

G:\ionic\btwork\platforms\android\cordova\node_modules\q\q.js:126
                    throw e;
                          ^
Error code 1 for command: cmd with args: /s,/c,ant,debug,-f,G:\ionic\btwork\plat
forms\android\build.xml,-Dout.dir=ant-build,-Dgen.absolute.dir=ant-gen
Error: G:\ionic\btwork\platforms\android\cordova\run.bat: Command failed with ex
it code 8
    at ChildProcess.whenDone (C:\Users\tomsong\AppData\Roaming\npm\node_modules\
cordova\node_modules\cordova-lib\src\cordova\superspawn.js:135:23)
    at ChildProcess.emit (events.js:98:17)
    at maybeClose (child_process.js:755:16)
    at Process.ChildProcess._handle.onexit (child_process.js:822:5)

check the version of Android SDK Build Tools installed (21). When I
uninstalled that (in Android SDK Manager) and left version 20 as the
highest installed version of the Android SDK Build-tools. It suddenly
worked…

thank you I have done it.