Commented...

Commented <plugin><groupId>ch.elca.el4j.maven.plugins</groupId><artifactId>maven-depgraph-plugin</artifactId><version>1.1</version</plugin> as it is not available into the Maven central repository.

frascati/pom.xml

@@ -136,10 +136,12 @@
       <!-- To use this plugin, type: 'mvn depgraph:depgraph' -->
       <!-- This plugin requires the 'dot' library, provided by the -->
       <!-- GraphViz software (http://www.graphviz.org ) -->
+<!-- 
       <plugin>
         <groupId>ch.elca.el4j.maven.plugins</groupId>
         <artifactId>maven-depgraph-plugin</artifactId>
       </plugin>
+ -->
 
       <!-- Generate Javadoc documentation -->
       <plugin>

pom.xml

@@ -282,6 +282,7 @@
           <!-- To use this plugin, type: 'mvn depgraph:depgraph' -->
           <!-- This plugin requires the 'dot' library, provided by the -->
           <!-- GraphViz software (http://www.graphviz.org ) -->
+<!--
           <plugin>
             <groupId>ch.elca.el4j.maven.plugins</groupId>
             <artifactId>maven-depgraph-plugin</artifactId>
@@ -291,6 +292,7 @@
             </configuration>
             <version>1.1</version>
           </plugin>
+ -->
       
           <!-- Used to create a binary distribution. -->
           <plugin>