When using JDK 1.3.1_07 or 1.3.1_08 as a target one, you might encounter the following error message trying to debug a project: "Java Virtual Machine Launcher - Could not find the main class".

These JDK version have a problem with a classpath when running in the debug mode. IntelliJ IDEA can't do anything about this issue, it's a JDK bug.

The solution is to rollback to JDK 1.3.1_06 or to use 1.4.x versions.