An issue that occurred recently for a number of WP users was that suddenly links, inlcuding menu links, to their Blog page resulted in an Error 404 page. The thread is here.
I, like some others, thought it to be connected to the recent WP upgrade. Maybe it is indirectly but I tired of waiting so started a program of plugin dactivations this morning. The very first one being WP Super Cache, resolved the issue.
I have suggested in the thread above that other users report back on whether deactivating WP Super cahe resolved the issue for them so you can get a handle on the extent of the issue.