Once the pressure is all the way down to zero, you remove the weight or petcock depending on which you are using (weights or gauge). Then you need to wait another 10 mins. before removing the lid. Sounds like there was still too much pressure in the canner? Seems unlikely that all those jars were defective. Were they canning jars or saved mayo type jars?
http://nchfp.uga.edu/publications/ug...s_canners.html
Also, not clear on your wording. Did you process for 90 mins, then let the pressure go down? (that would take considerably longer than 90 mins total). Or did you process for less time than that?