Clear Blue Advanced OPK Error

Looking for some feedback! I've heard that the clear blue advanced OPKs are the most accurate out there so I switched to the brand a couple of months ago.  But both months I used it, I got an error after 2 days of "high fertility" (blinking smiley face) and never got the "peak fertility" (solid smiley) ... the first time I just figured it was a defective strip or something but 2 months in a row? Anyone know what this means?