I have a number of lists scattered throughout my site collection that have recently stopped indexing for Search, and there are errors in the crawl log for these lists of "Error in the Site Data Web Service. (The given key was not present in the dictionary.)" After the error the lists are no longer present in the index. The lists in question are in different subsites, don't have unique permissions and don't seem to have anything of note in common. The site collection does indeed have a top-level site and none of the posts on this error in any forum that I've found seem to apply here.
Running MOSS SP2 and we've had no configuration changes that I'm aware of. Ideas?