Following is the output I first received, which is comparable to the
problem others mentioned:

Tag library requested that is not present: 'maven' in plugin:
'maven-xdoclet-plugin-1.2'
java.lang.NoSuchMethodError:
xjavadoc.XClass.getTransformedName()Ljava/lang/String;


The 'NoSuchMethodError' of the xjavadoc lib implies the signature is not
available in that xjavadoc library.  So, I updated that jar to version
1.1, as opposed to the 1.0.2 as mentioned above in dependencies.  It worked.

Your config may not require this specific change, but this error (and
java errors in general) could very well be caused by incompatible lib
versions, or even subversions.

best...