I found the problem: the classpath is not set correctly in falcon-mxmlc.jar.
Here is the content of MANIFEST.MF: Manifest-Version: 1.0 Ant-Version: Apache Ant 1.8.2 Created-By: 1.6.0_35-b10 (Sun Microsystems Inc.) Sealed: false Implementation-Title: ActionScript Compiler - MXMLC Command Line Compi ler Implementation-Version: 2.0.0.0 Implementation-Vendor: Apache Software Foundation Main-Class: org.apache.flex.compiler.clients.MXMLC Class-Path: compiler.jar - Raju
