Error message while working on an external site: what's wrong?

I tried to install modx (MODx version 0.9.6-rc3) on a website. The installation process went smoothly. Using a firefox browser, I tried to access and edit the homepage. After editing, when I tried to save the page, it returned the following error message:

Not Acceptable
An appropriate representation of the requested resource /modx-0.9.6-rc3/manager/index.php could not be found on this server.

Apache/1.3.37 Server at www.arin.1gb.cc Port 80

What does this message mean? Can I work around the problem?

Kind regards,
Arin Basu

Apache’s mod_security strikes again Check here for more info: http://wiki.modxcms.com/index.php/What_is_mod_security_and_how_does_it_affect_me