All, Today protobuf used by Drools/jBPM was upgrade to version 2.5.0. If you only use the marshalling code, you don't need to do anything. Maven should automatically download the new version and use it. If you do protobuf development and need to re-generate the protobuf classes from time to time, here is a reminder of how to configure your environment. Please note that the configuration of the plugin (specially for the jBPM module) is extremely important, or you will start to have all kinds of errors and will not know why. 1. Download and install protobuf compiler from: http://code.google.com/p/ protobuf/downloads/list 2. Install protobuf-dt eclipse plugin as detailed here: http://code.google.com/p/protobuf-dt/ 3. Configure the destination directory to generate the java files as detailed in step 2 here: http://code.google.com/p/protobuf-dt/wiki/IntegrationWithProtoc Set the "Java Output Directory" to: src/main/java 4. VERY IMPORTANT FOR JBPM: jBPM Flow project has a .proto file that extends the data types defined in the .proto file in Drools Core, so you need to configure the protobuf import path as detailed here: http://code.google.com/p/protobuf-dt/wiki/ImportPaths Add the following import paths to the jbpm-flow project: ${your drools-core project in eclipse}/src/main/resources ${your_drools_flow_project}/src/main/resources After doing that, when you edit and save the .proto files, eclipse will automatically compile and regenerate the java source code for them.-- Edson Edson Tirelli JBoss Drools Core Development JBoss by Red Hat @ www.jboss.com