Today I received error on my vm summary page in Vsphere web client: The data service timed out because a back-end task took more than 120 seconds. See the vsphere-client-virgo.log for more details.
Just before that I removed a test vcenter server, which was connected to my PSC on production Vsphere instance.
You need to remove a stale vCenter Server from your SSO environment, use the cmsso-util. It may takes a long time but does the job.