This usually is due to a mistake in the configuration.
To troubleshoot this please look here for tips:
Running "dmesg" on the controller should give you clues where the mistake is. Maybe also your drive needs some startup parameters to work properly. This you can find in its documentation.
The SDOs currenly need to be added by hand, so it is correct that the list is empty for a new configuration. If you add SDOs to the list, they will show up in Motorcortex, so you can issue a read command (setting "read_sdos" to 1 in the parmater tree) to read the values from the drive. Or modify their values, the new value is then sent to the drive via the mailbox automatically when the corresponding parameter in the tree is written to.
I hope this help you with debugging this.