I'm a long time listener, first time caller, having problems with a site I'm administering (rather than my own, which seems to be working well).
Running: WP 3.5.1 (installed 22.3.13), no plug-ins, TwentyTen theme.
Have checked up-to-date server: running PHP 5 and updated MySQL
Despite following instructions on the 3.5 Master List -i.e deactivated all plug-ins, acivating Twenty Ten (and have tried with TwentyTwelve, TwentyEleven too, just in case) I still get a 404 when trying to post (draft or publish) with images/media.
I've tried the WP_TEMP_DIR fix to the wp-config.php file suggested in the Master and the CONCATED_SCRIPTS fix suggested in other similar posts for media issues.
Neither have worked.
I've flushed caches, de-activated plug-ins through the FTP/server as well as through wp-admin - no change.
The update was a manual update of 3.5.1 in the first place after running into troubles with automatic update from 3.3.1.
I checked the file permissions before that update and everything seemed to be in order.
A suggestion that works would be MUCH appreciated.