Engine Start Blocked by Immobilizer .. Huh?

my mk4 golf once done the exact same thing, glow plug light flashed and wouldn't start, not even cranking. I was stuck at work so I kept trying and eventually it worked like normal, never fixed it as it only done it once and never again, though i did swap the key for the spare!
 
fault from transponder to car
nothing to do with battery in key

prob just gremlins
 
Are you local? i could check your transponders are sending and recieving signal. more likely a sticky relay or switch unless the cluster is on its way out.