socket: too many open file descriptors

[pollex]

Hello,
Running bind9 9.3.4-2etch3 on Debian etch 4.0(last stable version with
apt-get install bind9) and I continue to get "socket: too many open
file descriptors" messages.

my ulimit -a:
core file size          (blocks, -c) 0
data seg size         (kbytes, -d) unlimited
max nice                        (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) unlimited
max locked memory       (kbytes, -l) unlimited
max memory size         (kbytes, -m) unlimited
open files                      (-n) 24576
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) unlimited
max rt priority                 (-r) 0
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) unlimited
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

And we already tried the selectest tool:
./selecttest
selecttest: nsocks = 4093, TEST_FDSETSIZE = -1, FD_SETSIZE = 1024,
sizeof fd_set = 128
created 4093 sockets, maxfd = 4095
FD_CLR test...OK
FD_SET test...OK
select test...OK

Any ideas?
Thanks in advice