It sometimes happens that some pages of QueueMetrics cannot be opened; they crash during the JSP compilation stage with a "JasperException" showing that the page cannot be compiled.

This is often caused by having the wrong system-wide charset encoding, so that the source files cannot be read correctly from the disk.

To check if this is your case, you should go to the Licence Page, click on the [...] link to see all Java properties and check the value of file.encoding that should be ISO-8859-1. If it's anything else, it is a good idea to tell the Java subsystem to use this as a default encoding. To do this, you have to set an environment variable before starting Tomcat:
JAVA_OPTS="-Dfile.encoding=ISO-8859-1 -Xms256M -Xmx512M"
export JAVA_OPTS This tells Java to start by using ISO-8859-1 as the default file encoding and use a minimum of 256 megabytes and expand the memory pool as needed up to 512 megabytes. You should also set this in the /etc/init.d/queuemetrics startup file, so that it's set system-wide when QueueMetrics starts.

See also FAQ: Out of memory error for more information on Java setup variables.