I had this same issue after moving VMs to new hardware and upgrading to vmx10 vHardware. Here is how I resolved it;
1. Shutdown the VM.
2. vMotion to another host. (Not sure if this step is necessary but I did it)
3. SSH into the host the VM is now on and browse to the Datastore that the VM is on. cd vmfs/volumes/Datastore/VM_name
4. list (ls)
5. look for any -ctk.vmdk. All will need to be renamed. See step 6.
6. mv vmname-ctk.vmdk vmname-ctk.old
7. Power On VM and then try to migrate.
This is a known issue affecting vCenter 5.1 and 5.5
The issue is resolved in VMware vCenter server 5.1 Update 3 and VMware vCenter server 5.5 update 3.
For work around please go through this KB articles: