Couple of things I've noticed about adsense - have no idea if they apply here, but maybe it hasn't been considered.
If the colour of the links and whatnot are two similar to what you are using on the site (particularly if they are positioned to look much like links) the ads can fail to appear. This has happened to me a few times and I've changed the colour to have them up and working again within a few minutes.
Another thing - I've also had pages fail to display adsense where the content is exactly the same as another page serving adsense (botched url structure in my case).
I assume you've tested these things - but figured it may be worth mentioning anyway. You never know.
If the colour of the links and whatnot are two similar to what you are using on the site (particularly if they are positioned to look much like links) the ads can fail to appear. This has happened to me a few times and I've changed the colour to have them up and working again within a few minutes.
Another thing - I've also had pages fail to display adsense where the content is exactly the same as another page serving adsense (botched url structure in my case).
I assume you've tested these things - but figured it may be worth mentioning anyway. You never know.