Are you accessing the vCenter server or ESXi host.
Is your host and vCenter are healthy and accessible via webclient ?
Have you tried to accessing server from other machine using vsphere client ?
similar issue was found in other link, check if this helps
am Tried both vcenter and esxi host.
Same issue follows
in other client working fine. issue is only in my system
Was it working fine before? Have you tried uninstalling and reinstalling the client ?
i tried reinstalling the client same issue follows
What's your OS version? .NET version? Looks like SSL/TLS issue. Did you have any disabled TLS version in the local OS registry or in your host using the vmware TLS configuration utility (1 , 1.1 etc)?
ref:
Transport Layer Security (TLS) registry settings | Microsoft Docs
Managing TLS Protocol Configuration with the TLS Configurator Utility
window 8.1
share the steps to check tls and ssl settings in my system