[Zope] more __len__ errors

I am having a intermittent problem with ZCatalog(I think). I have a couple of products that are catalog-aware and have been working. Then, out of nowhere if I call <dtml-in "Catalog(meta_type='object')"> I get a __len__ error, when a few minutes before it worked. I looked at the undo list to see if I have done anything to cause it but could not find anything. I delete the cataloged objects as well as the objects themselves and re-create them. Same problem. Here is the TB: