Problems with VirtualBox and ServerDatacenter

Question

I was able to install SERVER_EVAL_x64FREE_en-us.iso and then convert it to ServerDatacenter using a purchased Product Key, but there were issues with VirtualBox. I've now deleted the installation and recreated it, but when I try to convert it again to ServerDatacenter, I get an error with the old Product Key. It's as if it's already been used.