I was hit by that a few days ago on a different project, and it's an endorsed problem, due to a wrong Xerces version. Now, don't ask me how to fix that in eclipse, but if you can make ant use Cocoon's xerces you should be fine.
This is a very weird error. I am compiling and debugging Cocoon CVS with Eclipse 3.0 M7 and no problems reported.
I don't think the problem is releated to Xerces in ant 1.6.1:
Eclipse 3.0 M7 uses Ant 1.6.0 and XML4J 4.0.13 based on Xerces 2.0.0 <website>http://www.alphaworks.ibm.com/tech/xml4j</website> Cocoon 2.1.5-dev (CVS) uses Ant 1.6.1 and Xerces 2.6.2
I will review the build system if there can be a potential problem.
I don't understand your argument. I'm almost sure it is an endorsed libs problem as almost everything related to XML and JDK 1.4 is a endorsed libs problem :-( I don't see how Eclipse (or the ant process started from inside Eclipse) should make an exception for this.
Joerg
