The IRS sent me a notice telling me I owe taxes for 2010 on a cancellation of debt according to a form 1099-c they received. I never received this form and don't know of any cancellation of debt in that time frame. What can I do?

Did the notice indicate who cancelled debt for you, such as a credit card company or home equity or mortgage loan? The IRS should have provided a number to call for questions - give them a call and see what they say. Perhaps if they tell you the name of the company that issued the 1099-C it would remind you.