I'm converting VM's from xenserver to vsphere 5.1 and multple VM's will hang at random percentages, they never fail. I have converted several VM's just fine but have been running into some that never finish. The firewall and UAC are turned off. I have tried using the converter locally on the server and remotely but still have the same affect. I am also using the 5.1 converter.
Welcome to the Community - There are many things that can cause this including network bandwidth to something running on the source server like a back up -