Not Getting a Result

I have used the Clear Blue Advanced Digital Ovulation Test that gives you your 4 most fertile days and overall I'm pretty happy with it but I have one complaint/question. Pretty much at least once with each test I've bought, I will not get a result from the test. The symbol is supposed to start flashing within 1 minute and it doesn't flash at all, therefore I do not get a reading. I do nothing different when this happens. I take the test exactly how I am supposed to. These kits are not cheap so I am not happy that this keeps happening with pretty much everyone I buy at least once. Does anyone else have this happen? Can you please tell me why this happens when I take the test exactly how it says. Thanks.