Based on your question, I'm guessing you're in bash 3.2 or earlier, where
$ echo $BASH_VERSION 3.2.39(1)-release $ cat /etc/issue Debian GNU/Linux 5.0 \n \l
your "hd <(echo -en \\0{0..3}{0..7}{0..7})" is expanded as if you had typed
"hd <(echo -en \\0000) <(echo -en \\0001) <(echo -en \\0002) ..." and
runs into the FD exhaustion issue Chet already described.
thanks for this and your previous post. bye
