Monitor reading fertility test error multiple days

I have just started using the monitor this month. The first two days it read low fertility. The third day is was high. The past three days however have all read that there was a fertility testing error. I have done the exact same thing that I have been when the tests were working. I'm really getting frustrated as I should be ovulating right now. Please give me another reason besides me using it wrong (which I know I'm not). Do I have a faulty monitor? Please help!