I am using the maven indexer to fetch the maven index from the maven central repository. Since I updated from org.sonatype.aether to org.eclipse.aether and from maven 3.0.5
This error is caused by the Maven 3.1-alpha-1 migration from Sonatype Aether to Eclipse Aether, which is an incompatible change for some plugins.
To support this change, new versions of the affected plugins have been published which work both with Maven 3.0.x and 3.1.x. A list of affected plug-ins and their minimum needed version is available at https://cwiki.apache.org/confluence/display/MAVEN/AetherClassNotFound