I got the same problem. The key would not turn, so obviously something was blocking the latch.
Thanks to amire's suggestion I was able to open the rear seat. It turns out that I had put some screw drivers folded in a plastic bag under the seat and that was obstructing the latch and key would not turn.
Darkrider5000: I'm glad that you opened your rear seat going thru those plugs. This was my second option, but I had installed rails to mount a GIVI box and it would have been very hard to remove them and re install them back.
I'll never again put nothing under that seat! Live and learn