Looks like some bad XML snuck in. This from a fresh CVS checkout:

$ ant refdoc
refdoc:

clean:
 [delete] Deleting directory /opt/seam/doc/reference/build

all.doc:

lang.all:

lang.docpdf.prepare:
 [copy] Copying 33 files to /opt/seam/doc/reference/build/en/pdf/images
 [java] Error on line 1402 column 19 of file:/opt/seam/doc/reference/en/modules/components.xml:
 [java] Error reported by XML parser: unexpected characters in element end tag (expected "varlistentry")
 [java] Transformation failed: Run-time errors were reported
 [java] Java Result: 2

... etc ...