I don't know about runing this on a mainframe but I get that message when it doesn't release a port after I shut down and start it up again. Maybe your not looking at the right port in netstat in which it's complaining about.
Thanks for your reply.
The port issue turned out to be a configuration problem. Now I can get it to start, open the ports, and serve pages, but all the HTTP I/O appears to be in the EBCDIC codepage, thus looks like garbage on the browser and browser requests return 404, presumably due to misinterpretation of the ASCII URLs.
I have been working with the file.encoding value but have not had any luck in resolving this problem.