I recently had an issue where a ESX host had stopped responding in VC, I tried disconnecting and re connecting but I was unable to connect, getting an error stating “Unable to access the specified host, it either does not exist, the server is not responding or there is a network problem”. I tested to ensure DNS resolution was working correctly from both the ESX hosts and virtual center and tried restarting mgmt-vmware and vmware-vpxa but the problem still existed. Checking with VMWare Communities forum I found the following resolution.
remove vc agent on the ESX Host by doing the following
rpm -e VMware-vpxa-2.0.x.xxxxx(get the full packaged name by typing command “rpm -qa | grep -i vmware-vpxa)
Then reconnect to the host from the virtual center.
Virtualised Reality 
its superb thanks a lot for info
I’m glad it was of use