help

hi in the last 2 months i have bought 2 overvaluation kits and it both packets 2 have cane up with a errors. i have been using this product for 5 months now and Neva have had one test come up like this but to have 2 from 2 different packets its a bit strange. i discarded what was left and went and purchased a new one and have had no trouble this time. is there any thing u can do to help me .