I run an SMP with my friends and NiftyCarts recently joined the fold. I've noticed that we can't teleport with carts, which is unfortunate since we do use waystones and teleport commands. It would make trade more interesting if we could bring carts with us!

Could you please provide a crash report for the game crash

If I'm more specific - if you use commands to teleport, the cart will get blocked by something and not come with you. If you use warpstones however, your entire game will crash.. :(