I had an application that suddenly would fail on any page that used a style sheet approval.css. In the designer I could open the css and it looked fine so I decided to delete the css and recreate it. So I deleted it and then created a new css called approval.css, and when I opened it it contained all of the code from the original css. So I deleted all the code and just added some test lines. Closed the css and then re-opened it back to the original state. Tried all the usual fixup, compact, clean etc. Nothing worked. Tried creating a new copy and that did not work either. The only way I could find to get back to a working copy was to create a new blank DB, then manually copy all the design and documents into it (not the css though). Created a new css and copied the original code into it.
It now works, but lost the better part of 2 days trying to get it fixed. Some how there was some internal corruption that just could not be fixed by the usual methods. It is one of those things that is fixed, but have no idea what caused it, nor how to fix it other than start over from scratch. Never happened before, and hope it never happens again. I know this does not help you with your problem,but you are not alone. Fortunately, these sorts of things don't happen often in N/D - my DB was very much still in test mode so there were multiple program failures as I debugged it so that could have been part of the problem.