It might happen that your project has the same artifactId for different groups. To avoid file name clashing, specify the full file name mapping.
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-ear-plugin</artifactId>
<version>2.7</version>
<configuration>
[...]
<fileNameMapping>full</fileNameMapping>
</configuration>
</plugin>
</plugins>
</build>
As a result, each artifact file name will be prefixed by the groupId to avoid clashes. There is also a no-version file name mapping if you do not want to get the version in the file names.