I did a (maven) checkout of one of the maven plugins (to see how it worked) and it failed to build. I tried building it from the commandline and it worked fine; a refresh in eclipse on the project showed no errors.
But when I opened one of the of the source files, there were compile errors showing in it. Cause: the maven build generated some sources in target/generated-sources. Fix: go to those sources and right click -> Build Path -> use as source folder. Several of our sandbox projects have generated sources, for things like XMLBeans. I've posted a query about this in the m2eclipse users list. -Marshall
