The lock on our Thule roofbox has jammed with key in it, it has locked, but key not turned enough to remove it. We cannot open it, or lock it enough to remove the key. Any tips to try to free it up?

I did a lot of research on forums about this and wanted to consolidate the results:
1. Don't use WD40, it attracts dust and grime later, use Silicon Spray or graphite dust
2. The main reason I'm posting, once it's free to open, lubricate behind the sliding locking bars with Silicon Spray, this helps A LOT.
3. Also consider what I did which helps 99% of the rest of the way: buy a couple feet of PVC, large enough to cover the sliding locking bars, cut it in half the long way, attach it to the box over the locking bars (I drilled holes and used zip ties).
The only remaining issue I have now is if I pile stuff too high and it puts upward pressure on the box lid, so don't do that. ;-)

As to the PVC, I think it was 1", and in fact it was not really big enough to completely cover the locking bars, so I didn't tighten the zip-ties down all the way, if I did it again I'd get bigger pipe or heat it and flatten it out a bit, but I just tested this setup on a 1200 mile trip and it worked great, noticeably smoother opening and closing.

I had the same issue. Do not try and remove the key with either side of the carrier up. Close (slam) the carrier closed and then the lock will turn back and the key will come out.

Make sure the hinges at either end are clear of stuff.

I know this is old but there doesn't seem to be much on the web about this common problem. If your roof box lock appears to be jammed, key stuck in, broken off etc here is my advice based on what happened to mine. Basically the issue is not the lock but the sliding locking bar inside the box, when you lock or unlock the lock you are just turning a small Lever inside the locking bar mechanism which slides the locking bar left or right to clamp or release the 3 hinge pins on the lid. The locking bar slider is aluminium, about 4 feet long and a lot for the little key to move, especially when dirty, clogged with sand etc. I'm my case both sides were seized solid - it was assumed that the locks themselves were seized solid these were forced until the keys snapped off. One bit I picked out with a paper clip, the side I had to drill the whole barrel out. Fortunately my lid was open so I was able to free the sliders inside - wd40, gently tapping the end of the slider back and forth until it was free. New lock barrel, sorted!