Can't save Profile when rich-text formatting in the Pre-Form Help box

[stfrequency]

Hi all,

CiviCRM newbie here with an odd issue. I've recently discovered that I can't make any edits to an existing Profile. When I open it, make any edits (or not) and try to save it, I get this error on a white page:

Forbidden
You don't have permission to access /administrator/ on this server.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

After much troubleshooting, I've learned that there may be many things the system doesn't like now about the content in the Pre-Form Help box in this particular Profile. But on a basic level, I cannot even create a new Profile from scratch and save new text to the Pre-Form box if there are certain rich-text formatting edits made (Bold, Italics, etc). It gives me the error and won't let me save. If I remove the formatting, I can save it fine. There are other examples of things that seem to bring up this error, but this is the most obvious.

This is a new issue, as we were previously able to create Profiles with such formatting and save them. Recently we've had an IT guy do some work on streamlining our URLs across the site, so maybe this has something to do with it? Any suggestions on what might be going on are much appreciated!

ST
www.rockymountainseeds.org