I'm having the same problem with saving map editor files.
when I save the map it gets to "Auto-compounding: Finalizing...", gives an error, and won't save changes.
The editor log has lots along these lines:
"00:02:15.608 : <ERROR> [ufs] Failed to mount ../../base_map in read-write mode."
My sky is fine though. If you hit A too many times it turns the sky red - it's a select-all function or something. Have you checked that? Just hold down A. Happens to me every so often, so I keep a note of the fix.
