I believe head is going to require j2se 1.4
since it will implement j2ee1.4
It hasn't gone far down the road towards that goal.
You can probably fix the build by
adding the jaxp classes to the offending build.xml
I think HEAD still builds with 1.3 though... ?
Are you sure you don't have conflicting xml libs somewhere in your jre/lib/ext for instance?