Quick note:
You can experience error like this one:
creation of Image Preparation VM Failed, message Citrix.ManagedMachineAPI.ManagedMachineException: No hosts available
while using XenDesktop7 and scvmm 2012 sp1. In our case it turned out that scvmm had hyper-v hosts in 'update needed' state. After an update had been delivered, MCS started working again.
