While trying out Maven-3 (alpha-4) against our project, Maven-3 showed up that our pom.xml of the jboss-ejb3-build has duplicate dependency elements with different versions for the same artifact(s):
...
<version.org.jboss.common.core>2.2.14.GA</version.org.jboss.common.core>
...
<version.org.jboss.reflect>2.0.2.GA</version.org.jboss.reflect>
...
<dependency>
<groupId>org.jboss</groupId>
<artifactId>jboss-common-core</artifactId>
<version>2.2.5.GA</version>
</dependency>
...
<dependency>
<groupId>org.jboss</groupId>
<artifactId>jboss-reflect</artifactId>
<version>2.0.0.CR1</version>
</dependency>
...
<!-- JBoss Common Core -->
<dependency>
<groupId>org.jboss</groupId>
<artifactId>jboss-common-core</artifactId>
<version>${version.org.jboss.common.core}</version>
</dependency>

<!-- JBoss Reflect -->
<dependency>
<groupId>org.jboss</groupId>
<artifactId>jboss-reflect</artifactId>
<version>${version.org.jboss.reflect}</version>
</dependency>

Notice that the pom declares dependency on jboss-common-core for 2 different versions (2.2.5.GA and 2.2.14.GA). Same is the case with jboss-reflect. Maven-2 doesn't show up this as an error (it should have), but Maven-3 rightly shows this as an error and fails to build:

[ERROR] The build could not read 1 project -> [Help 1]
[ERROR] The project org.jboss.ejb3:jboss-ejb3-build:1.0.8-SNAPSHOT (/home/jpai/business/jboss/wc/jbossas/projects/ejb3/trunk/build/pom.xml) has 2 errors
[ERROR] 'dependencyManagement.dependencies.dependency.(groupId:artifactId:type:classifier)' must be unique: org.jboss:jboss-common-core:jar -> version 2.2.5.GA vs ${version.org.jboss.common.core}
[ERROR] 'dependencyManagement.dependencies.dependency.(groupId:artifactId:type:classifier)' must be unique: org.jboss:jboss-reflect:jar -> version 2.0.0.CR1 vs ${version.org.jboss.reflect}
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/ProjectBuildingException