building server and client product gives error "Java returned: 13"

When I want to build the server.product or the swingclient.product according to http://www.globalqss.com/wiki/index.php/IDempiere/Creating_Installers_from_Eclipse I get the following message:

org.eclipse.core.runtime.CoreException: D:\NewOSGI\IDempiere\org.adempiere.server-feature\product.ant:22: Java returned: 13

The error message was first mentioned in 2012-09-10 in https://groups.google.com/forum/#!topic/idempiere/gCGs8RdTOqU

As far as I can say the error message comes and goes for unknown reasons. I have a workspace where is sometimes shows up and after trying a thousand things like workspace clean etc. it goes away. After changing something in the feature project it comes back. This needs some more research.

This issue has two parts: One part is that there is an error. The other part is that this error does not give a meaningful error message (this is why I fight for two weeks with this). The "error 13" leads by google to an eclipse issue about a wrong binary architecture. I believe this is a wrong path and the error lies somewhere in the idempiere build configuration.