Inconsistent results using Advanced Digital ovulation tests

I have been using the Clearblue Advanced Digital Ovulation tests (purple ones) for 7 months now. I had the tester and a few test strips left over from the month before. I started testing 6 days ago with a brand new box of sticks and tester. On days 1 & 2 I got low fertility (circle) on days 3-5 I got high fertility (blinking smiley faces). Today when I tested I pulled out the old tester and strips form the month before just to check if i was getting an accurate reading. The test blinked and indicated a new cycle like it should since I had not used it in for them 3 days. The test came back low fertility (circle). A few hours later i decided to test with the newer tester and stick i had been using this whole cycle and it came back peak fertility (smiley face). If i was in the high fertility zone or even in the coveted peak fertility time then both test should read such and not give me two different readings. I really hope I have not been wasting money on this product and we still are not pregnant.