Hyper-V Conversion fails with the following error:
Final error: 0xe000a400 - Failed to create the standby virtual machine required for warm conversion.
Final error category: Resource Errors
For additional information regarding this error refer to link V-79-57344-41984
This can occur when the System Logon Account on the media server doesn't have permissions on the Hyper-V server. If for instance the Media Server and Hyper-V server being converted are on different domains.
Add permissions to the Hyper-V server so that the System Logon Account on the media server has the neccessary rights to connect to the Hyper-V server.
Bengine debugs on the Media Server may show
 2012-05-01T14:38:17.345 [ndmp\ndmpcomm] - ERROR: 69 Error: Windows LogonUser API failed.
 2012-05-01T14:38:17.350 [ndmp\ndmpcomm] - ERROR: 69 Error: Windows LogonUser API failed.