[Users] Little issue

Dear All, My engine.log file continues to give the following error: 2014-03-25 10:04:55,381 WARN [org.ovirt.engine.core.vdsbroker.VdsManager] (DefaultQuartzScheduler_Worker-35) Failed to refresh VDS , vds = 497c0af3-4897-46f4-bffa-049bcd0ae713 : buran, error = java.lang.NullPointerException, continuing.: java.lang.NullPointerException 2014-03-25 10:05:10,705 WARN [org.ovirt.engine.core.vdsbroker.VdsManager] (DefaultQuartzScheduler_Worker-42) Failed to refresh VDS , vds = 497c0af3-4897-46f4-bffa-049bcd0ae713 : buran, error = java.lang.NullPointerException, continuing.: java.lang.NullPointerException 2014-03-25 10:05:25,945 WARN [org.ovirt.engine.core.vdsbroker.VdsManager] (DefaultQuartzScheduler_Worker-9) Failed to refresh VDS , vds = 497c0af3-4897-46f4-bffa-049bcd0ae713 : buran, error = java.lang.NullPointerException, continuing.: java.lang.NullPointerException 2014-03-25 10:05:41,189 WARN [org.ovirt.engine.core.vdsbroker.VdsManager] (DefaultQuartzScheduler_Worker-72) Failed to refresh VDS , vds = 497c0af3-4897-46f4-bffa-049bcd0ae713 : buran, error = java.lang.NullPointerException, continuing.: java.lang.NullPointerException 2014-03-25 10:05:56,449 WARN [org.ovirt.engine.core.vdsbroker.VdsManager] (DefaultQuartzScheduler_Worker-67) Failed to refresh VDS , vds = 497c0af3-4897-46f4-bffa-049bcd0ae713 : buran, error = java.lang.NullPointerException, continuing.: java.lang.NullPointerException 2014-03-25 10:06:11,763 WARN [org.ovirt.engine.core.vdsbroker.VdsManager] (DefaultQuartzScheduler_Worker-5) Failed to refresh VDS , vds = 497c0af3-4897-46f4-bffa-049bcd0ae713 : buran, error = java.lang.NullPointerException, continuing.: java.lang.NullPointerException 2014-03-25 10:06:27,164 WARN [org.ovirt.engine.core.vdsbroker.VdsManager] (DefaultQuartzScheduler_Worker-49) Failed to refresh VDS , vds = 497c0af3-4897-46f4-bffa-049bcd0ae713 : buran, error = java.lang.NullPointerException, continuing.: java.lang.NullPointerException 2014-03-25 10:06:42,463 WARN [org.ovirt.engine.core.vdsbroker.VdsManager] (DefaultQuartzScheduler_Worker-76) Failed to refresh VDS , vds = 497c0af3-4897-46f4-bffa-049bcd0ae713 : buran, error = java.lang.NullPointerException, continuing.: java.lang.NullPointerException 2014-03-25 10:06:57,814 WARN [org.ovirt.engine.core.vdsbroker.VdsManager] (DefaultQuartzScheduler_Worker-1) Failed to refresh VDS , vds = 497c0af3-4897-46f4-bffa-049bcd0ae713 : buran, error = java.lang.NullPointerException, continuing.: java.lang.NullPointerException 2014-03-25 10:07:13,167 WARN [org.ovirt.engine.core.vdsbroker.VdsManager] (DefaultQuartzScheduler_Worker-49) Failed to refresh VDS , vds = 497c0af3-4897-46f4-bffa-049bcd0ae713 : buran, error = java.lang.NullPointerException, continuing.: java.lang.NullPointerException 2014-03-25 10:07:28,504 WARN [org.ovirt.engine.core.vdsbroker.VdsManager] (DefaultQuartzScheduler_Worker-81) Failed to refresh VDS , vds = 497c0af3-4897-46f4-bffa-049bcd0ae713 : buran, error = java.lang.NullPointerException, continuing.: java.lang.NullPointerException 2014-03-25 10:07:43,887 WARN [org.ovirt.engine.core.vdsbroker.VdsManager] (DefaultQuartzScheduler_Worker-93) Failed to refresh VDS , vds = 497c0af3-4897-46f4-bffa-049bcd0ae713 : buran, error = java.lang.NullPointerException, continuing.: java.lang.NullPointerException 2014-03-25 10:07:59,305 WARN [org.ovirt.engine.core.vdsbroker.VdsManager] (DefaultQuartzScheduler_Worker-90) Failed to refresh VDS , vds = 497c0af3-4897-46f4-bffa-049bcd0ae713 : buran, error = java.lang.NullPointerException, continuing.: java.lang.NullPointerException Over and over again... Any ideas? Kind regards, Koen