ADB errors

1. ADB error: device not found

http://stackoverflow.com/questions/21408674/adb-error-device-not-found

2. ADB error: device offline

It is because of an old version of ADB (e.g., 1.0.29). It requires 1.0.31 or greater. 

http://stackoverflow.com/questions/10680417/error-device-offline