You may need to uninstall vpxa if you experience these symptoms:
ESXi host shows as Not Responding in VirtualCenter
ESXi host shows as Disconnected in VirtualCenter
Cannot connect ESXi host to VirtualCenter
When attempting to add an ESX host to VirtualCenter, you see an error similar to:
Unable to access the specified host, either it doesn’t exist, the server software is not responding, or there is a network problem
To uninstall the vpxa agent:
From the main yellow and gray screen on the ESXi host, press Alt-F1.
At the next screen, type:
When prompted, enter the root password.
Execute the following command:
Note: The vpxa agent automatically re-installs once the ESXi host is connected to vCenter Server.
Source: Vmware KB