Can't backup config in cnmatrix ex-2028-p

Hi, I am trying to backup up configuration file but it is giving this error


What software version is installed on the switch?
If this is a brand new switch or you had never saved the configuration on the switch, please execute the command ‘write startup-config’ to create/save the config file on the switch. You can try to back up the config file after this.
Also, make sure the file iss.conf exists in the tftp root directory on the TFTP server.

Version 4.0-r4
I saved the iss.conf file on the switch using the switch web gui

I presume the switch can ping the tftp server’s ip address. Also make sure there is no firewall application running on tftp server that will block the operation.
By default tftp server only allow upload of files that already exist. Please create the file iss.conf in the proper tftp directory on your TFTP server. You can just copy any local file and rename it to iss.conf.