I had multiple T3 slips downloaded from CRA and only 1 of them was giving me problems with box 52 and 53 not adding up to box 21, which is strange! However, I read from a previous post that if you round the numbers in boxes 52, 53 and 21 up or down and make all 3 boxes add up to numbers WITHOUT decimals then it fixes the problem. I did that and it worked. Give it a try before printing and mailing it in.
