ThinApp Factory 404 problems due to Single Sign-On?

Like a lot of people I'm having 404 issues when trying to add a workpool for ThinApp Factory in my company's vCenter.  I'm starting to wonder if my problem is due to vCenter 5.1 and Single-Sign On.  Is anyone out there using Factory with 5.1?

I've reviewed these articles and haven't found anything to help:

https://blogs.vmware.com/thinapp/2012/06/step-by-step-setup-of-thinapp-factory-in-vsphere-using-the-executable.html

https://vstorage.wordpress.com/2012/06/16/thinapp-factory-fixing-adding-workpool-error/

https://blogs.vmware.com/thinapp/2012/06/http-404-and-500-errors-when-adding-work-pools.html

I'm not using domain\username.

I've tried several different accounts including the service account and other vcenter administrator accounts.

The Factory VM is not an a DVswitch.

I haven't moved Factory since installing the appliance.

I'm using fully qualified domain names