When Congress is unable to complete work on an appropriations bill by the beginning of a fiscal year (FY) -- October 1 -- it passes what is called a continuing resolution that allows the agencies involved to continue spending at the same rate until an appropriations bill is passed.
Take a look at the status of the appropriations bills for FY 2010 which begins in 16 days. Social Security is covered by the Labor-HHS bill. It does not seem likely that all of these bills will be passed by the end of the month. Continuing resolutions hamstring agencies. They make planning difficult.