If your F*EX installation does not work as expected then first look in:

$FEXHOME/spool/fexsrv.log	(log from fexsrv)
$FEXHOME/spool/fup.log		(log from fup CGI)
$FEXHOME/spool/fop.log		(log from fop CGI)

If this does not help, set in $FEXHOME/lib/fex.ph :

$debug = 1;

then you will get in $FEXHOME/spool/.debug/ for each download a log file
with detailed debugging output.

If this does not help at all, contact me :-)
framstag@rus.uni-stuttgart.de