Nodes appearing but when clicked "page not found"
I had this problem, it only affected certain nodes. When investigated in db all values corresponded between node and node revisions tables so I initially assumed it wasn't related to values in those tables.
Checked url_alias table and all seemed well there too, site is multilingual so checked the variables table for discrepancies between multilingual paths auto values for custom content types and all was also well. Rebuilding the menu router didn't help either. I already tried resetting all node access permissions as suggested here. Honestly I was just about out of ideas, then thankfully I came across this post :D 
The problem had come from where i had imported some node content from a custom module i wrote to ingest nodes from xml (which worked fine) but since the import was done the user account which had done the import had been removed. This meant all the multilingual imported nodes were still linked to that, now non-existent user account's uid.
A simple sql query in phpmyadmin set all my nodes to be owned by admin (uid:1)

UPDATE node set uid = 1;
UPDATE node_revisions set uid = 1;

This fixed my perplexing issue. I propose a patch so that if a user account is removed Drupal optionally checks all nodes belonging to that user and updates them to uid: 1 so nodes added by a deleted user account aren't suddenly inaccessible to the rest of the site including uid 1 (admin). 
This was frustrating as a sensible sort would naturally assume that uid 1 will always have view/edit access to any node content on the site regardless of if it is, disabled, enabled or added by some mugwump.
I wish you good Drupaling!