There is a problem at the school with the way that user directories are mounted and the way that Tomcat tries to access your user directory.
Your user directory is accessed via /aul/homes/username. Your directory is not available all the time. When you make an access through /aul/homes/username, the school's operating system makes your directory available for about five minutes. After five minutes of inactivity, your user directory will be made unavailable. It is similar to a screen saver: after an inactive period, your screen changes to the screen saver - when there is activity, then your screen reappears.
The problem with Tomcat is that it doesn't play by the rules. It doesn't access your directory via /aul/homes. Instead, it goes directly to the disk where your data is stored. Most of the time this data is unavailable. Since Tomcat doesn't use /aul/homes, the operating system does not make your data available.
The solution is to first make a reference to some file using /aul/homes/username before calling Tomcat. The simplest way to accomplish this is to create a home page on the www.aul.fiu.edu server and to add a hypertext link from that page to your Tomcat host.
http://ocelot.aul.fiu.edu/~username
http://www.aul.fiu.edu/~username
http://studentXX.cgs4854.cs.fiu.edu/~username