Meu Java EE proj constrói bem, mas ao tentar executar obter seguinte erro:

gert@gert-VirtualBox:~/workspace/CDBOOKSTORE$ mvn exec:java 
[INFO] Scanning for projects... 
[INFO]                                       
[INFO] ------------------------------------------------------------------------
[INFO] Building CDBOOKSTORE 0.0.1-SNAPSHOT 
[INFO] ------------------------------------------------------------------------ 
[INFO]  
[INFO] >>> exec-maven-plugin:1.2.1:java (default-cli) @ CDBOOKSTORE >>>    
[INFO]  
[INFO] --- maven-dependency-plugin:2.8:copy (default) @ CDBOOKSTORE ---
[INFO]  
[INFO] <<< exec-maven-plugin:1.2.1:java (default-cli) @ CDBOOKSTORE <<<    
[INFO] 
[INFO] --- exec-maven-plugin:1.2.1:java (default-cli) @ CDBOOKSTORE ---
[INFO] ------------------------------------------------------------------------ 
[INFO] BUILD FAILURE 
[INFO] ------------------------------------------------------------------------ 
[INFO] Total time: 2.505s [INFO] Finished at: Fri Nov 08 14:01:40 EST 2013 
[INFO] Final Memory: 9M/21M 
[INFO] ------------------------------------------------------------------------    
[ERROR] Failed to execute goal org.codehaus.mojo:exec-maven-plugin:1.2.1:java (default-cli) on project CDBOOKSTORE: The parameters 'mainClass' for goal org.codehaus.mojo:exec-maven-plugin:1.2.1:java are missing or invalid
-> [Help 1]

Mas na minhapom.xml arquivo (que eu editei seguindo um exemplo de livro do Java EE), euter especificou omainClass config:

 <?xml version="1.0" encoding="UTF-8"?> 
 <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
     <modelVersion>4.0.0</modelVersion>

     <groupId>org.aptovia.javaee7</groupId>
     <artifactId>CDBOOKSTORE</artifactId>
     <version>0.0.1-SNAPSHOT</version>
     <packaging>app-client</packaging>

     <name>CDBOOKSTORE</name>

     <properties>
         <endorsed.dir>${project.build.directory}/endorsed</endorsed.dir>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     </properties>

     <dependencies>
         <dependency>
             <groupId>javax</groupId>
             <artifactId>javaee-api</artifactId>
             <version>7.0</version>
             <scope>provided</scope>
         </dependency>

         <dependency>
            <groupId>org.jboss.weld.se</groupId>
            <artifactId>weld-se</artifactId>
            <version>2.1.0.Final</version>
         </dependency>

     </dependencies>

     <build>
         <plugins>
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-compiler-plugin</artifactId>
                 <version>3.1</version>
                 <configuration>
                     <source>1.7</source>
                     <target>1.7</target>
                     <compilerArguments>
                         <endorseddirs>${endorsed.dir}</endorseddirs>
                     </compilerArguments>
                 </configuration>
             </plugin>
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-acr-plugin</artifactId>
                 <version>1.0</version>
                 <extensions>true</extensions>
                 <configuration>
                     <archive>
                         <manifest>                            
                             <mainClass>org.aptovia.javaee7.CDBOOKSTORE.Main</mainClass>
                         </manifest>
                     </archive>
                 </configuration>
             </plugin>

             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-dependency-plugin</artifactId>
                 <version>2.8</version>
                 <executions>
                     <execution>
                         <phase>validate</phase>
                         <goals>
                             <goal>copy</goal>
                         </goals>
                         <configuration>
                             <outputDirectory>${endorsed.dir}</outputDirectory>
                             <silent>true</silent>
                             <artifactItems>
                                 <artifactItem>
                                     <groupId>javax</groupId>
                                     <artifactId>javaee-endorsed-api</artifactId>
                                     <version>7.0</version>
                                     <type>jar</type>
                                 </artifactItem>
                             </artifactItems>
                         </configuration>
                     </execution>
                 </executions>
             </plugin>

              <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>exec-maven-plugin</artifactId>
                <version>1.2.1</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>java</goal>
                        </goals>
                        <configuration>                         
                            <mainClass>org.aptovia.javaee7.CDBOOKSTORE.Main</mainClass>
                        </configuration>
                    </execution>
                </executions>
             </plugin>

         </plugins>
     </build>

 </project>

Também parece OK de acordo com isto:https://www.mojohaus.org/exec-maven-plugin/usage.html

Eu fiz um mvn limpo, reconstruído, mas ainda recebendo esse erro. Realmente não tenho certeza do que está acontecendo :(

Qualquer ajuda muito apreciada!