I feel like I am having this very same problem. I have sent in a support ticket to my webhost and they are pretty reluctant to disable mod_security is there something else that can be done that does not affect the security of the server?
Thank you.
Hello
[color=#333333][font=arial, sans-serif][size=4]I got [/size][/font][/color][color=#333333][font=arial, sans-serif][size=4]the exact same problem[/size][/font][/color][color=#333333][font=arial, sans-serif][size=4]. [/size][/font][/color][color=#333333][font=arial, sans-serif][size=4]Please give [/size][/font][/color][color=#333333][font=arial, sans-serif][size=4]specific [/size][/font][/color][color=#333333][font=arial, sans-serif][size=4]instructions [/size][/font][/color][color=#333333][font=arial, sans-serif][size=4]what to do.[/size][/font][/color]
Please read the thread! There are several possible problems/solutions. Specificly posts 5, 9, 10, 13, 17 and 20.
It is possible it could be caused by any number of things but most tend to point to mod_security.
This error also occurs if you have any ad blocking extension or plugin running in your browser. After I disabled it for my domain everything went back to normal.
brandonvd’s suggestion works perfect also on other websites I’ve had problems with. Just make sure you replace the domain.com with yours 