Admin@system-domain can't log in to Vcenter server

I installed SSO on the Virtual Center server in our DR environment and then upgraded the Web Client.

When I log in to the Web Client as Admin@system-domain I see the following error message displayed:

Login failed due to invalid credentials for one or more vCenter Server systems:

I found this searching by searching for this message but it doesn't explain my issue as SSO and the web client are installed on the same server.

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2044531

Any ideas? Could this be normal as Vcenter hasn;t been upgraded to 5.1 yet?