Not Acceptable! An appropriate representation of the requested resource could not be found on this server. This error was generated by Mod_Security

I'm new to moodle environment and I'm having this error: > Not Acceptable! > > An appropriate representation of the requested resource could not be > found on this server. This error was generated by Mod_Security. I haven't done anything, I'm just viewing the registered users in my website:<br> http://www.joyfementira.com/dnsc/it14lms<br> I've noticed that my profile picture is not properly loaded so I clicked on it (picture's position), and after that the error came out. What probably caused this error and how would I fix it?