Try the following :
1. Run the following command.
2. Increase ADB connection timeout.
Change the ADB connection timeout from 5000ms (default) to say 15000ms.
You can change the ADB timeout at location,
Window > Preferences > Android > DDMS > ADB Connection Timeout (ms)
3. Restart Your Device
If your working on a device this trick works sometimes, Just restart your device.