On Fri, 26 Feb 2010, Mathieu Suen wrote: > (external-call "_uc_uc_test" :unsigned-byte -567 :unsigned-byte) -567 is not an UNSIGNED-BYTE, emphasis on "un". Unsigned bytes have to be positive. See http://www.lispworks.com/documentation/HyperSpec/Body/t_unsgn_.htm Adlai