Hello,
Check your partitions and make sure that you have quotas enabled on them. (/etc/fstab). You can also check your /usr/local/directadmin/conf/directadmin.conf file to make sure that the quota_partition=<path> is set to the correct partition. (the partition with the user's home directories).
Also, make sure that you have the edquota program, as that's what DA is using. It's returning a non-zero value, so DA spits out the error.
John