Go to Advanced Settings and change the password like it says and use winscp and connect to the pbx and change the ownership to asterisk of etc/dahdi/system.conf
I don’t want to change the password. I’ve had to. And I just hate changing defaults. You never know what it can break. My PBX is well protected and unrreachable from the outside.
That looks like a bug in the way the file validation is done. You can remove that warning by just creating the file (touch /etc/dahdi/system.conf) and the next version of Dahdi Config will have that bug fixed.