Did you ever come up with a solution to this problem? I'm having the exact same trouble: green light flashes, goes solid, chlorine generation takes place for about 2 minutes, then code 90. Looks like an air pocket is forming in the chlorine generation chamber. With the saltwater system turn off, running just the filter pump, no air pockets form.
BTW--I doubt it's your pump, because I'm using an Intex 1500 GPH pump.