High failure rate on test sticks

I started using this (on a 20 pack) 7 days ago. Yesterday, I had one test stick fail/error. This morning, I has *six* fail/error (so glad I pee in a cup....) and never was able to get a result before I had to leave for work. I kept the test strip in the sample for the 15 seconds and kept the test flat. Why is there such a high failure rate on these test sticks when I am following the directions?