Retrieving the COM class factory for component with CLSID {XXXX} failed due to the following error: 80040154

I developed a Windows service using C#.NET to generate PDF report. To generate PDF file I am using a third party dll. The application is running in my Windows XP platform. When I deployed the service in Windows Server 2008 64 bit version, I got this error: Retrieving the COM class factory for component with CLSID {46521B1F-0A5B-4871-A4C2-FD5C9276F4C6} failed due to the following error: 80040154. I registered the DLL using the regsvr32 command. I able to see this CLSID in the registry. But the problem persists. What could be the problem?