The problem is in plexus. The XPP parser doesn't support entities.
A solution is to modify plexus to use http://woodstox.codehaus.org/

I don't think this will be fixed for beta-3 but we need to update the docs:
http://maven.apache.org/maven-1.x/reference/backwards-compatibility.html and http://maven.apache.org/maven-1.x/faq.html#using-entities.

We have to modify modello (and not plexus) to use woodstox

Need more time to check woodstox.

what about using the modello-plugin-dom4j or modello-plugin-jdom instead of xpp3?

I'll try them. Thx for the idea.

I need these issues to be solved to build modello

Needed to resolve relative entities

It's now fixed. We use the stax reader/writer generated by modello. To close this issue we just have to wait for the releases of : modello 1.0-alpha-14, maven-modello-plugin 1.0, maven-model 3.0.2.
We'll update our dependencies and it will be good.

Fixed with maven-model 3.0.2