TylerJohnston on "[Plugin: WP Super Cache] 404 When saving Additional CNAMES"

Sorry if this has been asked before I could not find it in the forum. Everything works great however when I try and save Additional CNAMES I get a 404 page not found and nothing saved. I am in a multisite setup. I get the same thing when adding Additional CNAMES to a subsite. Any suggestions?
Many thanks.

http://wordpress.org/extend/plugins/wp-super-cache/