From Cristina Belderrain
I've observed this error happening on December 11. Unfortunately, I haven't kept a copy of the logs and they've been wiped out when I reinstalled Tomcat. So I'll try to leave here the config data you need:

Which version of Magnolia: 3.0.1 CE
Your operating system: XP Pro (localized to Brazilian Portuguese)
Memory size: 1 GB
Amount of memory allocated to java: 512 MB
Tomcat version: 5.5.20
Tomcat folder before: C:\Tomcat 5.5
Tomcat folder after: C:\Tomcat-5.5.20
JVM used by Tomcat is in folder: jre1.5.0_09/bin/client
JAVA_HOME points to folder: jdk1.5.0_09/bin

The space character was replaced by %20 in the logs... This gave me the first hint to what could be happening.

Hope this helps,

Cristina

Here's an interesting bit of logs:
WARN info.magnolia.cms.util.ClasspathResourcesUtil ClasspathResourcesUtil.java(collectFiles:131) 12.12.2006 15:45:23 missing file: C:\tomcat%205.5.20\webapps
\magnoliaPublic\WEB-INF\lib\magnolia-module-workflow-3.0.1.jar
WARN info.magnolia.cms.util.ClasspathResourcesUtil ClasspathResourcesUtil.java(collectFiles:131) 12.12.2006 15:45:23 missing file: C:\tomcat%205.5.20\webapps
\magnoliaPublic\WEB-INF\lib\magnolia-taglib-cms-3.0.1.jar
WARN info.magnolia.cms.util.ClasspathResourcesUtil ClasspathResourcesUtil.java(collectFiles:131) 12.12.2006 15:45:23 missing file: C:\tomcat%205.5.20\webapps
\magnoliaPublic\WEB-INF\lib\magnolia-taglib-utility-3.0.1.jar
WARN info.magnolia.cms.util.ClasspathResourcesUtil ClasspathResourcesUtil.java(collectFiles:131) 12.12.2006 15:45:23 missing file: C:\tomcat%205.5.20\webapps
\magnoliaPublic\WEB-INF\lib\mail-1.4.jar