Got this while compiling my GWT app
Java.lang.NoSuchFieldError: reportUnusedDeclaredThrownExceptionIncludeDocCommentReference

It did not occur when compiling with previous GWT compiler, but occurred with 2.4.0. Another WTF?!?? -- code was unchanged.

A handy message on the GWT Google group says that the order of export put in place by Maven was guilty.
I up-ped the GWT dev and user JARs
 with my answer