OK, several points as a result of this.
Resin's "virtual host" mechanism (like Apache's etc.) is handled by the server itself. So, if you want to run two virtual hosts,
you should really configure a
single resin instance to serve both hosts.
If you want to run two separate Resin instances on a single computer you either have to run them each listening to different ports, or use a separate web server (for example Apache or IIS) to manage the "virtual hosts", disable the direct access to the Resin server, and only access Resin through the Apache or IIS plugin.
To check if this is the problem, look in Resin's log files for things like "unable to bind to port".