Certain WYSIWYG Fields no longer Saving

Hi there!

I have a site that has been running CMS since April, and within the last couple of days, certain WYSIWYG fields have just stopped saving. It looks as though text fields/boxes still work fine, but any changes made to a WYSIWYG field, after you click save, just disappear and the content reverts back to the way it was. Has anyone ever had this happen? I sent an email to server support to see if any changes had been made to the server the site is on - but I'm wondering if its a CMS issue, since only some fields were having this problem.

Thanks for your help!
Kelly