I just had the same problem after adding a new 5.1 U1 host to our cluster. The vnetwork configs were identical and yet I couldn't vmotion to the new host... It worked for 4 VMs and then nothing... They all failed at 14%.
After reading a few posts on here I asked my networking team to permit all vlans on the physical switch (dedicated cisco switches for vmotion in an C7000 enclosure) and it worked right away. They reconfigured the switches to permit on the correct vlans (same config as when it was not working) and it has been working flawlessly since... 