T3 indicates there is an error as box 52 and 53 must equal 21, which it does, but can't file because program stating there is an error. What's wrong?

Please try doing the review, and if it shows you the error, click on Resolve and re-enter the amounts on box 52 & 53. If that doesn't solve the problem, enter the sum of 52 & 53 into box 53 and delete the amount in box 52. The new capital gains rate is not going into effect this year, so both boxes are taxed at the same one-half (50%) rate.