Cannot migrate VM from 6.5 to 7.1

Try to migrate VM from 6.5 pool to 7.1 pool usin CLI
xe vm-migrate vm=IVC\ Proxy remote-master=10.5.12.199 remote-username=root remote-password=*****

This command end with error:
The server failed to handle your request, due to an internal error. The given message may give details useful for debugging the problem.
message: Xenops_interface.Internal_error("Unix.Unix_error(56, \"write\", \"\")")

Part of /var/log/xensource.log on XenServer 7.1
emphasized text