I'm experiencing the exact same problem with Mudbox 2013. Before, it allowed me to continue but after upgrading it terminates the program. There may be a conflicting file somewhere or something of the sort but I have no clue what it is. I tried uninstalling and reinstalling but that doesn't do anything.
I'm not sure if there are leftovers from Mudbox 2011 still on my system as there's a possibility there is. I had to delete the folder manually since it refused to uninstall on it's own.
Any ideas? I really would love to use it again.