When Maven tries to find out the available versions of commons-configuration on Maven central it downloads http://repo1.maven.org/maven2//commons-configuration/commons-configuration/maven-metadata.xml
Problem is that this file does only contain a subset of available versions:
So in our case Maven thinks 1.6 is not available on Maven central and does not download it.
Our build fails. We are not able to build.
Please correct the list of versions on Maven central in the above maven-metadata.xml.