In simple terms, it means the server was not able to locate the resource you requested. This can occur because of four reasons:

• The URL you typed was wrong or has a typo.
• The URL you requested could not be resolved with the current "docBase". If you are trying to run your own "web-application" please read the questions related to "installing your own web-application" in this FAQ.
• You're using JDK 1.1.x on a Windows platform. It's a known bug (see Readme) that the server doesn't serve files in this configuration. Use JDK 1.2.x instead.
• On a Unix platform, you are attempting to access a file that is a symbolic link.

The last two cases are caused by a test in org.apache.tomcat.core.DefaultServlet to see whether the absolute name of a file equals the canonical name. This test is intended to solve a serious security problem, where mixed case or additional characters in a file name can get Tomcat to serve the source file instead of the processed file for JSP files on a Windows platform. This test should be replaced with a solution that doesn't have the above side effects.