CSP Gateway Management via Managment Portal link returns a page with a '0' and nothing else

On one of our servers, when I am in Mgmt Portal and click the link for Configure / CSP Gateway Management, I get this url:

http://ipaddress.of.server:port/INSTANCENAME/csp/bin/Systems/Module.cxw?CSPSYS=0&CSPSYSreferer=_CSP.Portal.Home.zen

but the page displays a 0, and nothing else. Literally, just a 0.  This link works on our other servers, with the same URL.  Any idea why? 

Thanks,

Laura