If you get error while trying to login Vcenter via web UI and get this error.
If you click OK, you will find the Vcenter UI without any VMs. It will be all blank. You may need to check the service status of your Vcenter Inventory as the name suggests. In our environment, the Vcenter is an appliance. Also it is a VM. If your Vcenter is a Windows machine / VM then you can check services.msc.
To resolve this issue and you have Vcenter appliance. Open a Web browser and type the Vcenter IP with port 5480 (xxx.xxx.xxx.xxx:5480) and login.
Here you can start the inventory service as shown below:
Identify your Vcenter (Appliance) IP address:
Strangely though Vpshere client functions without any issue and only Web UI faces this issue. Login to Vsphere client, and open the Vcenter appliance console.
This is a simplest way. Click the Vcenter appliance in the Vsphere client and click summary. You can see the IP address.