Are you using Live 11 ? If so there is clearly a problem with this upgrade and the Keylab range. I'm trying to sort it out, but if you have 11, then its probably NOT the keyboard. test as follows.
1 Run a vst plugin in a virtual host like Nanohost. Does the missing key now play ?
2 Reinstall Live 10. Is this ok ?
If the answer to either or both is yes, It's almost certaing not the Keyboad.
Final poof; download a demo copy of Bomes Midi Translator Pro (google it) and shut lLive down and connect Bome. Press the key. Do you see note on/off? Yes, again the keyboard is good.