This was working a few days ago.  Now whenever I try to link a Case to a Product through a lookup field, the lookup window is empty, and the search block returns no records if I enter the name of a product.  The search block in the standard Products view works fine, but for some reason (probably something I did during customization of the Products entity) now the lookup list (whenever accessed from any other entity) is always empty.

Any ideas on what would have caused this.  As I said the lookup window for products was working great up until a few days ago.  Has anyone else had a similar problem with lookup windows going AWOL?