RHEV VM migration fails with "Returning backwards compatible migration error code"

Issue

• VM migrations were failing without providing any meaningful error.

• The Event Log in the RHEV Admin Portal showed;

Failed to migrate VM abc to Host xyz. Trying to migrate to another Host

• The vdsm logs on the source host showed;

Thread-12509491::ERROR::2016-12-22 09:49:56,307::migration::252::virt.vm::(_recover) vmId=`36710f55-4f25-4c80-912e-d7c9dfc87b99`::migration destination error: Fatal error during migration

• The vdsm logs on the destination host showed;

jsonrpc.Executor/0::DEBUG::2016-12-22 09:49:56,304::API::601::vds::(migrationCreate) Migration create - Failed
jsonrpc.Executor/0::DEBUG::2016-12-22 09:49:56,305::API::607::vds::(migrationCreate) Returning backwards compatible migration error code

• A side-effect of this is that a host can go into an ERROR state if more than a pre-defined number of these occur within a set period of time. Please refer to the following KBase article for more information.