If you have manually typed in your W2, make sure that you've entered the Box 12a ~ 12d correctly.
I made a mistake of putting "A" for the 12a code and "B" for the 12b, instead of actual code letters (A, AA, B, BB, etc). That messed up my whole federal income tax refund (Turbo tax actually told me I owe 2k in tax, but after correcting this, I got a sweet tax refund instead!)
So just in case, check your reported W2 section and make sure all amounts and letters for 12a/b/c/d are correct.
