The deployed Maven POM for Hibernate Entity Manager 3.3.1.ga incorrectly excludes the dependency upon the oswego-concurrent libraries (see below). This leads to a NoClassDefFound error:

nested exception is java.lang.NoClassDefFoundError: EDU/oswego/cs/dl/util/concurrent/ConcurrentReaderHashMap
Caused by:
java.lang.NoClassDefFoundError: EDU/oswego/cs/dl/util/concurrent/ConcurrentReaderHashMap
        at org.jboss.util.file.ArchiveBrowser.<clinit>(ArchiveBrowser.java:52)

I haven't yet determined how the Maven POMs are being managed by the Hibernate team, but they don't seem to be in Subversion; therefore, I've marked this trivial, although it is a little more than that for someone who is trying to use the Maven repository.

In any case, it should be easy to fix. More generally, it might be more correct to employ Maven's ranged version dependency syntax, instead of explicitly excluding other dependencies.

excerpt from http://repo1.maven.org/maven2/org/hibernate/hibernate-entitymanager/3.3.1.ga/hibernate-entitymanager-3.3.1.ga.pom
<dependency>
<groupId>jboss</groupId>
<artifactId>jboss-common-core</artifactId>
<version>2.0.4.GA</version>
<exclusions>
...
<exclusion>

<groupId>oswego-concurrent</groupId>
<artifactId>concurrent</artifactId>
</exclusion>
...
</exclusions>
</dependency>