If you encounter an
too many open files exception you usually edit
/etc/security/limits.conf and increase the value.
But on Ubuntu (10.04 LTS at least) this is ignored!
A workaround is to edit
/etc/init.d/tomca6 directly and set the limits
ulimit -Hn 16384 ulimit -Sn 16384
Usually this error occurs if you run a resource intensive app like alfresco share.