Well after one week of non stop troubleshooting.... I discovered that the issue is related to SSO, eventhough SSO was reporting authentication is successful.
So I removed the "admin" account from SSO users and rebooted the vcenter server things start working right away.... since I upgraded sso from 5.1 to 5.5 the old system-domain "admin" account was in there some how it was causing the issue.
Please update if someone else find different fix.