Why does vdsm fail to start during boot but can be manually started later on?

Issue

• Why do RHEV hosts fail to activate after being restarted?
• Why does vdsm service fail to start during boot?

# cat /var/log/boot.log:
[...]
Starting iscsid:                                           [  OK  ]
vdsm: Running mkdirs
vdsm: Running configure_coredump
vdsm: Running configure_vdsm_logs
vdsm: Running wait_for_network
vdsm: Running run_init_hooks
vdsm: Running upgraded_version_check
vdsm: Running check_is_configured
Traceback (most recent call last):
  File "/usr/bin/vdsm-tool", line 219, in main
    return tool_command[cmd]["command"](*args)
  File "/usr/lib/python2.6/site-packages/vdsm/tool/__init__.py", line 37, in wrapper
    func(*args, **kwargs)
  File "/usr/lib/python2.6/site-packages/vdsm/tool/configurator.py", line 108, in isconfigured
    if c.isconfigured() == NOT_CONFIGURED]
  File "/usr/lib/python2.6/site-packages/vdsm/tool/configurators/sanlock.py", line 87, in isconfigured
    .strip().split(" ")]
ValueError: invalid literal for int() with base 10: ''
vdsm: stopped during execute check_is_configured task (task returned with error code 1).
vdsm start                                                 [FAILED]

• Why doesn't that problem happen when I try to start vdsm service manually?