[Exim] what resource is lacking ?

I am getting this sort of error message before Exim crashes

1999-11-01 07:04:22 11iAqD-00078H-00 == joe@??? T=smtp defer (-1):
fork failed for remote delivery to domain.com: Resource temporarily
unavailable

This is a working configuration, that I just bumped up the number of
queue_run_max variable, and it's started crashing.

This is Exim 2.11, Linux 2.0.36, 256 meg of ram.

It originally bombed on too many open files, so I added this to the
initilization scripts.

if [ -f /proc/sys/kernel/file-max ]; then
    echo 16384 >> /proc/sys/kernel/file-max
fi
if [ -f /proc/sys/kernel/inode-max ]; then
    echo 24576 >> /proc/sys/kernel/inode-max
fi

So if anybody can clue me in on what sort of resource is the hold up, I
would appreciate it.

mark