Proxyed webmin and configserver firewall problem


I have setup webmin to display in a sub category by using the proxy methods. So that now users go to

and it will load webmin.

I have CSF (ConfigServer Security & Firewall) installed but the module has stopped working correcly. I can click on the module to load up the main modules screen, but as soon as i try to do anythink i receive a error message. I have provided a picture.