I read elsewhere that there was a proceedural problem with a Senate bill passed earlier. I think it may have been this one. As I understand it,.they added a tax provision to a bill from the House.
The Constitution requires revenue bills originate in the House. Whatever the House passed would have had to go back to the Senate to be approved before it went to 0bammy for signature
The procedural problem was with a food inspection bill - the House Dems sent it back via “blue slipping.”
http://en.wikipedia.org/wiki/Blue_slip
http://www.naturalnews.com/030588_Food_Safety_bill_blue_slip.html