The 0.10.0 version (current) of m2eclipse plugin has a bug for those sandbox projects using XMLBeans, which causes them not to build - it has something to do with the XMLBeans generating java sources.
The bug [1] has been fixed, or at least, worked around, in an update to the m2eclipse plugin, which you can get following the instructions in [1]. I tried it , and it works. After running a mvn install from a command line, if the project doesn't build in eclipse, right click the project, and select Maven -> update project configuration. -Marshall [1] https://issues.sonatype.org/browse/MNGECLIPSE-1694
