The error message seems to say that there has been a problem trying to "mount" the application, so as monroe said, there should be some kind of error in the Tomcat logs. If the app. wouldn't be tried to be mounted, it would say "File not found", but it says "resource is not available" and that usually happens if an exception is thrown when deploying the application.
The usual approach is stopping Tomcat, removing all logs, starting it and then trying to see where it tries to deploy the application if there is any error.
If no error is reported, it is difficult to know what happened, or is happening.
Regarding the versions... I have also been unable to find how to download a previous version, but you should be able to upgrade with the instructions found here:
http://www.jforum.net/doc/Upgrade
Good luck!
[originally posted on jforum.net by GreenEyed]