The other day I was upgrading a customer from vCenter 5.1 to vCenter 5.5. They also wanted to move from their current Windows 2008r2 server to a new Windows 2012r2 VM. The upgrade seemed to go quite nicely. Everything said "successful" at the end. Then I went to login to the web client to configure SSO. I tried to sign in with firstname.lastname@example.org and got the error "Failed to connect to VMware Lookup Service..."
Every blog post I looked at having to do with this error had to do with the vCenter appliance, which I wasn't using. However, I did find a few posts that pointed to regenerating the SSL certs for vCenter, especially if you changed the hostname or IP. I had changed it, of course, but before I did the install.
Two things that resolved the error:
1. Uninstall vCenter (just vCenter, not SSO or the inventory service). Then rename the SSL folder to SSL.old (c:\ProgramData\VMware\VMware vCenter\SSL). Then reinstall vCenter. This will create a new SSL folder with new certificates.
2. Uninstall and reinstall the Web Client on the vCenter server.
After doing these two things I was able to login to the web client properly.