Thinking about easiest to hardest FordDoctor, have you checked the php permissions. Maybe that style sheet is not writable by the server. If it is a new style sheet that may actually happen. Others would work because they were on that server before, but new ones may not be getting the permissions they need. Just my first thought as I read this post this morning...
That would also go with any graphics folders etc. that may be related to the style as well.
Just a starting point if you haven't checked that already.
