Plugin error: execution not covered by lifecycle configuration

I am trying to use the maven-warpath-plugin available here. But I keep getting an error in my pom.xml file that says:

Plugin execution not covered by lifecycle configuration: org.appfuse.plugins:maven-warpath-plugin:2.1.0:add-classes (execution: default, phase: generate-sources)

How do I resolve this? Here is my pom.xml snippet for the plugin:

<plugin>
    <groupId>org.appfuse.plugins</groupId>
    <artifactId>maven-warpath-plugin</artifactId>
    <version>2.1.0</version>
    <extensions>true</extensions>
    <executions>
        <execution>
            <goals>
                <goal>add-classes</goal>
            </goals>
        </execution>
    </executions>
</plugin>

Eclipse offers me a quickfox tip to "discover new m2e connectors" to resolve this error. I have installed most of the connectors available that seem to apply but the error is still there. Any ideas how I could make this work?