There was an error sending the request! (404 error)

Hi yea,
Just a quickie,

I get the following popupish error "There was an error sending the request! (404 error)" when I try

CMS Setup >Section Editors>dingdong

and try add a field/textfield to the current form

my question is, could this be an error relating to 

Security Modules: ModSecurity 2
Caching Modules: Zend OPCache

as both are totally highlighted in red. 

Regards and thanks for input

Kenny