Resolution:
This behaviour has been noticed in the Job Manager (Workflow Desktop) when Non-Default RV Parameters are being used.

The java console from the browser listed the following error:
java.io.IOException: Server returned HTTP response code: 500 for URL ...
         ...

And looking at the servlet engine logs it lists:
2004-09-27 19:52:24 ErrorDispatcherValve[localhost]: Remote Client Aborted Request, IOException: Software caused connection abort: socket write error
2004-09-27 19:55:30 StandardWrapperValve[icviewer]: Servlet.service() for servlet icviewer threw exception
java.lang.NullPointerException
    at com.tibco.workflow.viewer.WfViewerServlet.doGet(Unknown Source)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:740)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:247)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:256)
                     ...
                     ...

This problem seems to be resolved setting the IC_TIBRV environment variables.
If you are using non default RV parameters, you need to set the following environment variables -
IC_TIBRV_SERVICE  &ltPort Number>
IC_TIBRV_NETWORK  &ltLAN>
IC_TIBRV_DAEMON  &lttcp:Port Number>