DMZ Client Scheduled Backup Fails and Savegrp Cmd succeed.

I have a DMZ client which the port range 7937-9936 have been opened and the both client and backup server are able to communicate without any issue. The problem is the backup will fail randomly on the certain volume with 1 retry attempt error.. When i use savegrp -v -G < > cmd to run the backup, backup completed sucessfuly.. Any idea??