Resource temporarily unavailable

Hi everyone

From time to time i get the following error:
could not fork new process for connection: Resource temporarily unavailable

im using Postgres 7.4.5, with kernel 2.6.2

my conf is:

max_connections = 400

and system is:

www3:/etc/postgresql# ulimit -a
core file size (blocks, -c) 0
data seg size (kbytes, -d) unlimited
file size (blocks, -f) unlimited
max locked memory (kbytes, -l) unlimited
max memory size (kbytes, -m) unlimited
open files (-n) 1024
pipe size (512 bytes, -p) 8
stack size (kbytes, -s) 8192
cpu time (seconds, -t) unlimited
max user processes (-u) 256
virtual memory (kbytes, -v) unlimited

im totaly bogus, any ideas ?

Thanks
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