vSphere Center auto disconnect to ESXi host

Hi all!

I'm trying to use vSphere.

I install ESXi on a host.

I start vSphere Client and add this host to datacenter.

It's fine, I can work something on this host.

But after about 30s-90s this host auto disconnect.

I have to reconnect to this host to working continuous.

I searched and tried fix by "Restart Management Agents" follow this tutorial

http://kb.vmware.com/selfservice/microsites/search.do?cmd=displayKC&docType=kc&docTypeID=DT_KB_1_1&externalId=1003490

But It can't help me fix my problem.

This is screen log of vSphere Client

Please help me fix It.

Thanks a lot!