VMware backup fails with a 'You do not have access rights to this file' error. (4036465)

Backups fail with Log and trace messages like these. 

1] Error   2014/04/02 20:43:38   566   Data Plugin   NVBUSERVER   TaskID 1u Failed to open virtual disk

Module/Thread   Id    Code Time Message
VDDK    :05528  141       0 194323 Remote connect done
VDDK    :05528   36       0 194338 Failed to open vmdk
VDDK    :05528  138       0 194338 VDDK error encountered: code 13
VDDK    :05528  139       0 194338 Retrieving error message text
VDDK    :05528   52       0 194338 VDDK error message is 'You do not have access rights to this file'