Applications occasionally start showing "The document could not be autosaved" dialogs
It seems that this is actually a bug in Apple's sandboxing implementation. This means that none of the steps above should help. We had the same console output in one of our applications (including the inability to save text) and spent quite some time on finding the cause of the bug (see this radar). From what we've found out, it seems that after retrieving the recently opened documents for a number of times, the application cannot save files anymore because it does not get the permission to do so. You could try clearing the recently used documents menu, maybe this helps.