I’m using Debian Linux 7.0 (Raspbian Turnkey), Webmin 1.830 and theme-stressfree. I’ve tried several theme, but nobody works. Authentic Theme stuck on loading
People reported this error in the past and it was theme related. Search on forum there is a topic hot to manually install/update Authentic theme so you can switch to this theme. If is theme related this should solve your error.