Ancestry.com is offering free access to its U.S. federal census records through 06 July 2014, 11:59 P.M. U.S. Eastern Time. Some people are reporting access problems, an event that is far too common when Ancestry offers limited free access.
Ancestry also did maintenance late Monday night and this can lead to access issues.
If you can’t find someone on the Ancestry census records, check the other websites offering census records. My great-grandmother was mistranscribed in Ancestry’s 1940 census, but I found her correctly transcribed on FamilySearch.org. Using information from FamilySearch, I tracked her down on Ancestry and added a note about the correct spelling of her last name.