Message:
The connection to adb is down, and a severe error has occured.
You must restart adb and Eclipse.
Please ensure that adb is correctly located at '/.../.../android-sdks/platform-tools/adb' and can be executed.
Solve:
[OS - UBUNTU]
1) sudo ./adb kill-server
2) sudo ./adb start-server
[OS - WINDOWS]
1) adb kill-server
2) adb start-server