If you want to debug Maven execution in eclipse, here is how I did it, with mostly command-line tools (no Eclipse plugin used) (may be off at some points, I haven’t done that for 6 months):
* Run, from the command line, mvndebug in place of the mvn command. Maven will begin launching and wait for an external debugger to appear on a TCP port before resuming. Note the port number.
* Configure in Eclipse a custom, remote debug configuration. (See http://www.ibm.com/developerworks/library/os-ecbug/ , Remote debugging) – set the port number as the one used by mvndebug. Also put the source files that you will be using for debugging in the Debug configuration.
* Launch the remote debug configuration. Maven should resume and you will catch bugs in Eclipse.