Exactly. I learnt the hard way. I even saved the tune before i started tuning, tuned for a while then thought id turn off the lock. Then just cruising along i clicked write and guy looked at me and said, theres no power. I thought he was joking till we came to a stop on the side of the road.
I tried loading the original tune, i checked everything under the bonnet, then thought id try initialise before i called a tow truck. Started straight away. But the original tune was way out. Had to baby it, thought nothing of the lock so i unlocked them and did a bit more tuning, clicked write and bam no power, now that i knew what was causing it i stayed away, had to do a full tune.
Luckily Paulr33 had heard of this happening only a few times, so when i emailed him he could explain it.
Scary