Tomcat 4.0.x "Class org.apache.jsp.{Class} not found.

In Tomcat 4.0.x, all jsp pages are running as part of the org.apache.jsp package.
If you use any class that hasn't been imported, the jsp compiler is expecting it to be in the same org.apache.jsp package.

If a class does not belong to any package (so, for example, it is phisically located in WEB-INF/classes), it must be imported:

<%@ page import="MyClass" %>

This is different from previous versions of Tomcat where that esplicit import wasn't required (even if there were some cases where that wasn't completely true).