I’ve seen this several time where a given vSphere Web Client cannot connect to the vCenter server or SSO server.
It’s a simple fix, but one that frustrates you unless you already know the solution.
- Go to the vCenter’s VAMI interface - https://vcenter.fqdn:5480
- Note that the vSphere Web Client service is probably running fine.
- Stop / Start the vSphere Web Client Service
- Grab a coffee. It will take a few minutes for the vSphere Web Client to be initialized.