Ovulation test repeated error despite following instructions

I have diligently followed the instructions on the ovulation test kit but keep getting the same error message (b). I've even got someone else to follow the instructions and used a pot to collect a sample rather than peeing on the test. Is there a chance there's a problem with the device or tests?? I've only got 2 results out of 10 teats all the others have been errors. It's so expensive to keep getting errors.