And all of a sudden it works… Since I cannot edit my earlier post, I'll add a reply.
My real defect is with this plugin, I get the following result from an ANT script:
Buildfile: E:\notesdata\workspace\bosman1_2fBOSMAN\Product.ntf\ProductBuild.xml
main:
[eclipseexport] EclipseFileList.getFileResources: dir = E:\notesdata\workspace\bosman1_2fBOSMAN\Product.ntf\${project}\WebContent\WEB-INF
[eclipseexport] EclipseFileList.getFileResources: relativePath = WebContent/WEB-INF
[eclipseexport] EclipseFileList.getFileResources: WebContent/WEB-INF/ProductBuild.properties does not exist.
BUILD SUCCESSFUL
Total time: 264 milliseconds