Unable to save - strange error message. Help!

Hi there

I’ve been using MODx for the last four or so months and it has all run smoothly. However, tonight when I tried to save a page (whilst in Firefox) I got this message:

Not Acceptable
An appropriate representation of the requested resource /manager/index.php could not be found on this server.
Apache/1.3.41 Server at www.mywebsite.com Port 80

(note: website URL changed)

...and my page won’t save. So I tried in IE and got this message:

Internet Explorer cannot read this webpage format

My web pages are all displaying fine, but I am unable to alter any pages as I cannot save.  I really need help as I need to make changes to my site as soon as possible.

Can anyone through some light on why this has happened and how I can resolve it?

Many thanks in advance

Rachael 

I don’t recognize the errors but my initial thoughts are that it may be related to mod_security: http://wiki.modxcms.com/index.php/What_is_mod_security_and_how_does_it_affect_me

Does this happening when saving anything, or only with snippets and plugins?

Thanks for your reply. I’ll have a loiok at the link you sent. It is happening when I try and edit any web page. I can’t change my homepage or any other pages in my website as this error message means that changes are not saved. It’s very bizare that it just suddenly happened tonight after months of running fine.
Any suggestions out there?