When registering the Windows Rights Management Services (RMS) in Central Administration in MOSS, I received the "The required windows rights management client is present but the server refused access. IRM will not work until the server grants permission", even if I followed the 'To add SPS-SRV to the RMS Certification Pipeline' step from 'Deploying Windows Rights Management Services with Microsoft Office SharePoint Server 2007 Step-By-Step Guide'.
Solution: the Central Administration web application looks up in Active Directory the registered RMS service connection point and tries to access the ServerCertification.asmx web service which is in the C:\Inetpub\wwwroot\_wmcs\Certification folder. Give to the account of the Cenral Administration's application pool Read&Execute rights on the ServerCertification.asmx file.