I'm not sure when this issue actually popped up, but we're now getting 404 errors attempting to load the dashboard page on all of our non-domain-mapped sites (i.e., subdirectory sites only -- the ones that are mapped to domain names are still okay). To the best of my recollection, we haven't changed anything recently at the server level, nor has anything in WP been touched in quite some time, other than the most recent WP update. I did a quick rename of .htaccess but the 404 still occurs. Research on the problem has so far been fruitless. At this point we're stumped. Any suggestions would be appreciated.