I had the same problem today and eventually resolved it by following the recommended solution in this thread.
To quote CCIE17603....
~#~
The Fix: all you have to do is ssh into your host and run this command from the cli:
# vmkload_mod multiextent
Unfortunately after a ESXi host reboot the multiextent module unloads and you have to perform this again to get your Sims to boot. If anyone can find a way to make this persistent with a switch or write a script that makes it load upon host reboot. I'm sure everyone would be very thankful.
~#~
I'm running 8.3 RC1 on ESXi 5.5 U2. As soon as I'd done the vmkload_mod multiextent I was back in business.
Cheers,
Gerg