The usually the reason is the suction cups were not seated properly.

Step # 1

Make sure windshield was clean and does not have any bugs or contamination that would keep the suction cups from seating.

Step # 2

Make sure you use ample suction cup lubricant. The lubricant helps keep a seal on in perfect windshield such as sand blasted windshield.

Step # 3

If you use your tool on more than 1 chip and you leave the injector in the Crack Eraser tool make sure you un screw the injector and adjusting bolt back until they are flush with the tool. If either one is sticking out they will not let the suction cups seat all the way down to the windshield. Push firmly down when seating the cups to get all the air out. You will hear squishing sound until the cups are seated properly.  Double check by pushing on all the cups again you should not hear any squishing sounds again.

Step # 4

Make sure you only turn the injector and the adjusting bolt 2 to 3 turns after they touch the windshield. If you turn them to far down the suction cups will pop off from to much pressure.