By default, system calls and file input/output are disabled in MapleNet for security reasons. Allowing file I/O on a public MapleNet server can be a major security hole that could allow user submitted worksheets to read files on the server. In a controlled environment, it is possible to setup the server to allow file I/O but worksheets would have to be reviewed to ensure they do not compromise server security.
The restriction on file I/O can be overridden is by removing the -z option in the line
kernel.localhost.program_args=-noclient -jgui -z
and commenting out the line
in the file
where $TOMCAT is the Tomcat installation folder (e.g. C:\Program Files\Apache Software Foundation\Tomcat 7.0).