I stumbled upon the same solution that gvaiss found. If you play a file from the saved directory that comes up first, it will crash.
But I also found what seems to start the crashes for me: Having my HDD hooked up when starting WiiMC. Even if I unplug it, if it’s still in the same directory and I don’t change the shares, it will crash. I was hoping to try the betas, but the links are dead. I just updated to the newest version.