are you pulling timing when you spray? are you sure it is jetted properly? are you sure the solenoids dont stick? is it wired correctly? wet kit or dry? what aftermarket window switch are you using?

i mean im not exactly a zex fan or technician but a nitrous kit is pretty cut and dry simple. you dont just have 'bad luck' and blow a motor. you probably messed up the install somehow or the solenoid may have something lodged in it to keep it open.