if you have cpanel installed in a vps and quota is not working then this solution is for you:
1. shutdown vps
2. run: vzctl set <veid> –quotaugidlimit 500 –save
(500 is number of users/groups that will be accounted. i think 500 is enough for most users)
3. start vps
now in ssh console run
/scripts/fixquotas
that’s all.