hardware status error hardware monitoring service on this host is not responding or not available

Hi ,

we have this error in vcenter with hardware status in esxi in  version 4.1 , ww have  enviroment vcenter 5.5 u2 ,

Only problem in esxi version 4.1 and all esxi 4.1 are in DMZ , and work ok in 5.5 esxi hosts

Error in log vws.log .:

[2015-02-18 08:07:08,508 pool-30-thread-2  ERROR com.vmware.vim.cimmonitor.service.impl.CimMonitorImpl] CertificateException in thumbprint computing: msg: certificate bytes returned from VC is null,

StackTrace:

java.security.cert.CertificateException: certificate bytes returned from VC is null

  at com.vmware.vim.cimmonitor.service.impl.CimMonitorImpl.getHostCertThumbprint(CimMonitorImpl.java:588)

  at com.vmware.vim.cimmonitor.service.impl.CimMonitorImpl.createCimClient(CimMonitorImpl.java:726)

  at com.vmware.vim.cimmonitor.service.impl.CimMonitorImpl.createCimClient(CimMonitorImpl.java:874)

  at com.vmware.vim.cimmonitor.service.impl.HostRefresherTask.refreshHostInt(HostRefresherTask.java:205)

  at com.vmware.vim.cimmonitor.service.impl.HostRefresherTask.run(HostRefresherTask.java:118)

  at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)

  at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)

  at java.lang.Thread.run(Unknown Source)

[2015-02-18 08:07:08,515 pool-30-thread-2  WARN  com.vmware.vim.cimmonitor.util.ThumbprintTrustManager] Invalid SSL thumbprint. Expected: ,received: E0:D5:C5:63:E0:C5:5D:6A:8D:26:D4:D4:F7:80:5E:6D:FC:51:2E:98

[2015-02-18 08:07:08,515 pool-30-thread-2  WARN  com.vmware.vim.cimmonitor.service.impl.CimMonitorImpl] Couldn't contact CIMOM on esx99.domain.com/host-33928

We tried remove host and add again in vcenter , not problem in dns resolucion , open port 5989 in firewall . We are lost.

some idea ?

thanks very much