Thank you! I will try it with Meshmixer and will post the result in here. But atm I'm very busy. So this will likely not happen until the middle of next week.
Addition:
I've found an export function in CraftWare and gave it a try. After that both tiles appeared in Cura. As I've found a solution for myself, I won't give Meshmixer a try. But I bet, it would have done the same.