When apache reports no space left on device: couldn't create accept lock and you’ve checked both disk space and inode usage of disk and they both report as fine check active semaphores:

ipcs -s

If there’s high number of them, Apache probably hasn’t cleared up after itself and some semaphores are stuck. Clear them out with:

for i in `ipcs -s | awk '/httpd/ {print $2}'`; do (ipcrm -s $i); done

If you’re completely out of semaphores (some other apps using maximum number) you may consider tweaking kernel limits in sysctl.conf:

kernel.msgmni = 1024
kernel.sem = 250 256000 32 1024

then run sysctl -p to pick up the new limits.