Quirky permalinks problem
A short while ago I noticed that a few posts were suddenly returning a 404 and the standard Apache warning for no apparent reason (WordPress 2.6.3). At first I thought it was just one, but I eventually discovered two others, with no obvious pattern among them. I searched the forums and but didn’t find any reports that quite matched mine. Turns out the fix was to change the permalink setting back to the “default” option (in Settings → Permalinks), and then re-select the one I use, “month and name.” These threads contain suggestions for this: switching to default and then back to custom, though here the problem seemed to be affecting all posts.