Hey pdrace,
I'm assuming you can still login via the vSphere Client with that account. If so, check this out for the Web Client: VMware vSphere 5.1
I realize that's not a permanent solution, but it should work til the 5.1 upgrade for vCenter. I've never actually used SSO prior to 5.1 (actually I've seen many sites avoid 5.1 BECAUSE of SSO haha) so I'm not familiar with issues firsthand.
Hope that helps!
~Brandit