That's true - the taxable amount can't be more than the total that you received.
If your form really shows that the taxable amount is greater than the amount in box 1, then you need to contact the issuer to request a corrected copy.
If those two numbers are the same, then enter a number in box 2a that is a penny less than the number reported on the form. The program will round up to the amount listed on the form, but it will be less than the amount in box 1.