Essentially, if all you've lost is the Client Admin, then you should be able to just create a new client admin via the SEE Full Disk policies.
If you've lost the Management Server Password however, then things are a little more drawn out as there's no simple recovery. The below article describes the process of simply applying a new password and updating the existing clients to recognise that change:
http://www.symantec.com/docs/TECH153740