I got custody of my son in August of 2010. My X is telling me that by claiming him I am violating the IRS rule since I did not have him for more than 1/2 of the year. My tax person stated that this is not true and that I did not violate anything. My custody paper work does not identify who claims who, just who has custody. Did I do something wrong and is my tax person wrong?

Should I ammend my tax claim for 2010 and allow my X to claim the son? I just want to do the right thing. Thanks