I keep getting compiler error

I was trying to setup a domjudge on Digital Ocean Ubuntu Machine. I followed the guide till end. System is running smoothly except that when I try to submit an answer I keep getting this error. Would you please help, I can't fix it for 2 days. Compiling failed with exitcode 255, compiler output: /home/magnus/domjudge/judgehost/bin/runguard: creating cgroup: Failed to remove a non-empty group(50029) Try `/home/magnus/domjudge/judgehost/bin/runguard --help' for more information. Error: failed to set /sys/fs/cgroup/memory/domjudge/dj_cgroup_3376_1517615852/memory.memsw.limit_in_bytes: Cgroup, requested group parameter does not exist