Questionable Accuracy

I test my blood glucose several times each day (12-14). Several times in the last week, I've tested and received inaccurate results.

Inaccurate Test #1
One night, I came home after working out, and my blood sugar was low. I treated the low with 15g carbohydrate, waited a while, and made dinner. My pre-dinner reading was 174. So I gave a correction bolus & my dinner dose. Within the next few minutes, I realized it was rather strange that my BG was so high after exercise, so I immediately retested. My BG was 119--much lower than 174. So I checked again. The reading was 124. I think the 174 reading was way off. And to confirm, even after eating extra carbs at dinner, my BG went low later in the evening; I had given too much insulin based on a faulty reading.

Inaccurate Test #2
Just this morning, I gave a correction bolus for a BG of 223. I tested a little while later, and the reading was 247. I was frustrated, because I thought my insulin wasn't working. On remembering past issues with the Aviva meter, I rechecked my blood sugar. Sure enough, the recheck read 210, almost 40 points lower than 247! My correction ratio is 1 unit/50 points. An inaccurate reading like this could result in a mis-dose of insulin of almost 1 unit...which could be the difference between a normal BG and an episode of hypoglycemia.