x-rt.tld specifies org.apache.taglibs.standard.tag.rt.core.WhenTag instead of org.apache.taglibs.standard.tag.rt.xml.WhenTag.
Fixed - thanks.
i listed the wrong class. you might have caught it anyway, but it should be changed to org.apache.taglibs.standard.tag.common.xml.WhenTag. sorry.
Thanks again.