Switch User to SYSADMIN hangs. HOME returns to login with session no longer valid.

We are on EBS 12.1.3.  We recently loaded HRMS End of Year 2014 Update III and patch 20272072 in a test instance.  Staff are running through payroll steps for testing.  Yesterday I was able to login with my credentials, Switch User to SYSADMIN, then go into Workflow Administrator to forward timesheet approvals to the staff who were testing.

Today, if we try to do the same thing, the Switch User function hangs after you click on the icon for SYSADMIN.  If you try it again or just click HOME, it returns you to the login screen with the error:

    Your session is no longer valid or your logon information could not be reestablished from your session.