proc on /proc type proc (rw)
sysfs on /sys type sysfs (rw)
none on /dev type tmpfs (rw)
none on /dev/pts type devpts (rw)
none on /proc/sys/fs/binfmt_misc type binfmt_misc (rw)
Hmm, I don’t see a filesystem with quotas enabled there.
Are you by chance using a VPS? If so, what sort of VPS is it… OpenVZ perhaps? If so, OpenVZ doesn’t tend to support quotas very well, you might consider disabling them. You can disable them by going into System Settings -> Virtualmin Config, and setting “Set quotas for domain and mail users” to No.