On some systems, notably Debian, the Tomcat package is installed by default with Java security policies active; such policies are very restrictive and may block Tomcat when trying to access the database or read files from the local file system.
See the entry Running with Java security
for an example ruleset that applies to QM 1.4.5.
If this is not possible, you'd better install Tomcat fresh from the tar file as described in the User Manual.
See also the Tomcat Security Manager HOW-TO for a better undertanding of the security manager.