According to the DayWatch:
Supporters fell 21 votes short because they would have needed a two-thirds majority to bring the bill to the floor. Five Republicans--Sheryl Albers of Reedsburg, Brett Davis of Oregon, J.A. "Doc" Hines of Oxford, Terri McCormick of Appleton and Mark Pettis of Hertel--joined all Democrats in favor of taking up the bill.Remember that the bill passed the Republican-controlled State Senate with only eight votes against. I've written about it before here and here.
UPDATE: Carrie Lynch asks a good question.