Maven2 build fails with Invalid task 'Project' error

[INFO] Scanning for projects...
[INFO] ------------------------------------------------------------------------
[ERROR] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Invalid task 'Project': you must specify a valid lifecycle phase, or a goal in the format plugin:goal or pluginGroupId:pluginArtifactId:pluginVersion:goal

Log:

org.apache.maven.continuum.utils.shell.ShellCommandHelper:default - Executing: /bin/sh -c 'cd <working-dir> && mvn --batch-mode --non-recursive -Dcontinuum.project.lastBuild.state=10 -Dcontinuum.project.nextBuild.number=1 "-Dcontinuum.project.group.name=Default Project Group" -Dcontinuum.project.lastBuild.number=0 clean install'