I had a similar experience last week with my 45 mm Olfa. Used the third blade from a relatively new 5 pack. Wouldn't cut. Took it apart, checked to make sure there was only one blade, put it back together, and it STILL wouldn't cut. After several more frustrating minutes I took the next new blade from the pack, put it in and it cut like a dream! Then, carefully, I felt the edge of the other blade. It was not sharp AT ALL. As in defective. Only time I've had that happen, thank goodness.