For completeness I add my experience.
My server was a fresh ML install and the settings and data from a Lion server had been migrated onto it. Also prior to the migration, Server.app had been intalled and then deleted by deleting in LaunchPad.
I had the shake problem logging in, and a quick glance at the log showed this had something to do with a certificate. I checked out the System Keychain and there was an expired com.apple.servermgrd certificate which must have been transfered from the old server.
I tried the suggested remedy of relaunching the daemon, but the plist was missing.
The cure to these ills was to uninstall and reinstall Server.app. This created a new certificate and the plist file after which it all works great.
Incidentally worth mentioning is that the Migration Assistant moved everything from the old server including the OD master and the contents of /usr/local. It was very impressive but did need aroound 9 hours for 250GB.