I had the same problem. After speaking to several professionals, they all told me the same thing. Sanding the floors wil not ensure the removal of the adhesive. Use an adhesive remover. This is a very strong chemical. Apply the chemical with a roller and let it sit for approx 45 minutes. Leave the room due to the fumes. Also, leave a couple of windows opened. You then scrap up as much as possible. If you need to repeat the process, do so. You do not have to remove it all. You are now ready to sandy the floor. Good Luck!