When I try searching for objects in Inmagic Presto 3.5 within a date range I get redirected to the "We are sorry" error page. Here's an example search making use of the built-in DateCreated field on the built-in Profile object:
Profile.DateCreated=[20101201 TO 20101225]
The date format (yyyymmdd) is taken from the documentation. I've also tried ddmmyyyy and mmddyyyy.