There are been a number of posts from folks having similar problems with the new "flat key" locks from OnGuard and Kryptonite. I thought those "complaints" involved people who just were unfamilar with a new lock, or who had gotten a rare "defective" lock. Or, as Raiyn claims, maybe anyone who has trouble with a flat key lock is just "stupid".
My opinion changed when I put a "new" 2005 "flat key" lock on a bike today. It locked up smoothly. But, when I tried to unlock it, the key would not seat into the keyway. I could move the the key back and forth, but I could not open the lock.
Looking inside the keyway, I discovered the problem. The "flat" key inserts into a keyway that ranges from 5/8th inch deep to one inch deep (depending on the model and the thickness of the crossbar). That keyway is built with seven to ten thin metal plates layered in a stack. Each plates has a rectangular channel to hold the key. The top plate has two "channels" in its rectangular that engage with the two grooves on the sides of the flat key.
But, the top plates in the stack can turn independently of the other plates. If you insert the key and begin to turn it before the key has reached the bottom of the keyway, it may turn easily, but will not engage the bolts. Although the key moves, you can not lock or unlock the crossbar.
In my case, I was bending over the lock at an awkward angle, and I must have twisted my wrist just as I was pulled the key out of the lock. When I reinserted the key to unlock the bike, the key turned, but I could not unlock the bike.
So, what do some owners do when their lock refuses to open? They force the key deeper and forcibly turn the key. However, when key is "trapped" against the misaligned plates, the key will break. And, the reports of owners breaking the new "flat keys" are numerous.
Fixing a non-working flat key lock: shine a light into the keyway (some Kryptonite and OnGuard locks supply a lighted key). Insert the key 1/8th inch and align plate one with plate two, so they form a single rectangle. Then insert the key 2/8th of an inch and align the top two plates with plate three.
When every plate has been realigned with the one above it and below it, you will be able see a deep rectangle going down to the center of the crossbar. You can now put your key down deep enough into the keyway to engage the bottom plate and open the lock.
This "quirk" exists on EVERY model of the 2005 flat key Kryptonites and 2005 OnGuard locks. The designs of their keyways are very similar.
And, a bumpy road might misalign a plate, so be prepared. If you have a lighted key, keep it with you. If the key will not fully seat, or the key turns, and the lock does not open, take your time, and realign the plates one by one. Then your lock will open.
I'm beginning to miss my round key locks...