DB error

I save a post – either save and continue or just save – and this appears in the post preview window:
“Database error: [You have an error in your SQL syntax. Check the manual that corresponds to your MySQL server version for the right syntax to use near ” at line 1]
SELECT post_content FROM wp_posts WHERE id=
“
Everything still works fine, and I assume I’ve slipped up somewhere when poking around, but any clues as to which file I need to look in would be cool.
(I’ve got all the originals, but I’ve not the slightest clue how to run a ‘diff’ on them)