Getting a 403 error after submitting CKEditor with certain text

Hi everyone,

I have been using CKEditor (and FCKEditor before it) for a long time now and it's a great tool. I am however having an extremely strange problem that I just cannot get to the bottom of and it's driving me nuts! When i use a specific set of characters in CKEditor and submit the form I get a 403 error.

I have stripped back the page so the only thing on it is the CKEditor textarea and a submit button (and tried upgrading to the latest version of CKEditor) but always the same problem. I am having this problem on a shared hosting environment, when i try the same thing on another host (also shared) it works absolutely fine so i'm guessing there's some security setting on the server causing the problem but I cannot for the life of me work out what (and there's no useful info in the error logs).

When I enter the following source into CKEditor I get the 403 page:

BD varje l&ouml;rdag 17.00-18.30 om inget annat anges, boka genom UO <a href="mailto:test@domain.com">test@domain.com</a><br /><br /><br />

However if i remove the <br /><br /><br /> from the end of the string then it works fine and reloads the same page correctly (which is where the test form action points to). If i add in <p> tags anywhere into the source then this also causes a 403 error on submission.

It must be a security setting on the server but I just cannot work out what it would be? If anyone could shed any light on this or even suggest anything I could explore to try and solve the problem then it would be greatly appreciated as i'm stumped!

Thanks so much,

Dave