Page Not Found when changing 'Other Settings'

Hi

Having a little bit of trouble with my NextGen installation. Everything is working fine except for my ‘Other Options’; when I try to change any of the settings and when I click save I get brought to the front end of my site where I am told that the ‘Page has not been found’. Any suggestions would be appreciated.

Cheers
Will

https://wordpress.org/plugins/nextgen-gallery/