vSphere web Client says 500 SSO Error Null after reboot of vCenter Virtual Appliance.
Once you are connected to your vCenter Server Appliance
check your log file hostname# cat /var/log/vmware/vsphere-client/logs/vsphere-client-virgo.log
Reading the logs – The PSC and the VCSA time was off by 20 minutes.
I configured the NTP and rebooted the vcsa and the psc and the web client came back to normal.
thanks dear! fixed my issue as well. restarted my VMs before ntp server was powered up.