I've seen this message before when there was a problem with a rewrite. The bot was getting caught in a loop which in turn was generating a high volume of pages returning a 200 OK. I'd double check and make sure you don't have malformed syntax somewhere which is causing the bot to get hung up in some sort of black hole.
Did you make any changes since the time that message appeared? What does crawl activity look like? Do you see an initial spike and then lots of spikiness afterward? That could be a sign of a problem somewhere in the machine.