Well, it's my own server's save, but I was running a dedicated server. I also didn't have any custom bricks activated.
I did not alter the save or any of the .blb's at all.
Also I noticed that it only happens when I look in a certain direction, then the error pops up, crashing my game. So it might be a single particular brick, but I'm afraid to edit the save file in fear I'll break my save totally.
Also this line came before it, is it important?
setWheelPowered: wheel index out of bounds, vehicle has 14500488 hubs
I've gotten that line before, but not with this save. Must be an add-on screwed up or something...