The first issues that will arise after replacing the jars or after changing the version numbers in the pom.xml are unresolved package imports. This is due to refactorings that became necessary when the project grew. Most of these import problems can be resolved automatically by modern IDEs (Organize Imports). So, this should replace org.jboss.errai.bus.client.protocols.* with org.jboss.errai.common.client.protocols.* for example.
The following is a list of manual steps that have to be carried out when upgrading:
@ExposedEntity became @Portable (org.jboss.errai.common.client.api.annotations.Portable). See Marshalling for details.
The @Conversational annotation must now target the event objects themselves, not the observer methods of the events. So an event type is either conversational or not; you no longer specify that listeners receive arbitrary events in a conversational context. See the Conversational Events section of the CDI chapter for details.
Errai CDI projects must now use the SimpleDispatcher instead of the AsynDispatcher. This has to be configured in Messaging (Errai Bus) Configuration.
The bootstrap listener (configured in WEB-INF/web.xml) for Errai CDI has changed (org.jboss.errai.container.DevModeCDIBootstrap is now org.jboss.errai.container.CDIServletStateListener).
gwt 2.3.0 or newer must be used and replace older versions.
mvel2 2.1.Beta8 or newer must be used and replace older versions.
weld 1.1.5.Final or newer must be used and replace older versions.
slf4j 1.6.1 or newer must be used and replace older versions.
This step can be skipped if Maven is used to build the project. If the project is NOT built using Maven, the following jar files have to be added manually to project's build/class path: errai-common-2.x.jar, errai-marshalling-2.x.jar, errai-codegen-2.x.jar, netty-4.0.0.Alpha1.errai.r1.jar.
If the project was built using an early version of an Errai archetype the configuration of the maven-gwt-plugin has to be modified to contain the <hostedWebapp>path-to-your-standard-webapp-folder</hostedWebapp>. This is usually either war or src/main/webapp.