I am trying to find data at the block level or even block group level for the SF1 files and ACS 2010 or 2009. Just recently, two months ago, I was able to get this data but for some reason I am now only able to get it at the census tract level??? I have followed all the ways in which I am suppose to extract this data. Did this change?
I have seen this happen as well. You can download by Block Group then it will not be available in the Download Center any more. I believe you can grab the data you are looking for from the census American Community Survey (ACS) FTP site available through the Summary File Data page of their website, also as pointed out above important FYI - block GROUPS are the smallest level of geography census summarizes ACS data not Blocks - highest precision but least accuracy.