Sorry for the issue. I will post here when I have a better idea when we'll have the problem resolved, but wanted to let you know we are aware of the issue and are investigating it.
As mentioned elsewhere on the boards, it appears to be associated with the State field in 1900 and 1910 US Federal censuses only. You can enter county and city/township (without state) and be okay. You can also enter in State in the keyword field, which will help narrow down results until we get this fixed.
Search Product Team