There was in fact an error message buried in those details. There was a
java file which only contained commented out code, and so no class file
was made for it. That apparently ran afoul of the export validation
checks. When I used to compile and make jars with JBuilder, it didn't
mind the "empty" java file.
(It would sure be nice if Ant and these builders put the keyword "error"
in all error messages so you can find them. We sometimes comb Ant output
for ages trying to find out why it failed.)