The Cisco.Wireless.LAN device type in CatTools should be trying both of those commands for the 'Device.Backup.Running Config' activity, so if 'show running-config' isn't supported, then CatTools will automatically try show run-config' straight after.
However, a number of customers have said that the data which comes back from using these commands is not the FULL device configuration. There is also issues on some devices where they hang during the sending of the command output back to the terminal window.
Therefore, I would strongly recommend you try the Device.Backup.TFTP activity instead. I believe the output is in clear text (not binary like some devices) so the 'diff/compare' feature should still work.
In the Optiosn tab of this activity, enter the text config into the File to write to TFTP server field.