Hey
Try to open a browser on the Management Server and connect to the URL to see what happens. Could it be a firewall problem? Or are you using proxies that redirect the request? Also check the permissions to connect to the Orchestrator web service. See this post -> http://marcelzehner.ch/2011/11/12/news-in-scsm12-beta-8-permissions-for-triggering-system-center-orchestrator-runbooks/
If this still does not work, try the same locally on the Orchestrator Server itself (to see if firewalls are somehow blocking the access)
Cheers