+x+xTry using a small space heater and blow hot air into the bag to get it to go off. It might have been just too cool for it to cure properly?? I use an old previously used bag, drape it over the top of the infused part, put small clamps around the edge of the table and blow the heater in between the old bag and the new part. Looks like a balloon but then you are only heating the area inside the balloon and not the whole garage. It get's pretty cool where I am in the fall and winter and it works pretty well for me. If that doesn't do it in a couple hours then i'd probably call it a loss. I've had it happen before too. Not much you can do. You could never re-infuse it with sticky resin already on it.
So the first infusion that didn't go off turned out to be beyond recovery. I cleaned it out, cleaned the mould and started again with new hardener. This time it was spot on and gave me the result I wanted. I also used another useful tip given to me by a friend for infusion at this time of year and bought an electric blanket to wrap the infused part in to aid curing. Even on slow hardener it was rock hard in 24 hours flat, so all's well that ends well and I have my seat base done! Picture attached ( the dull spots are PVA still to be washed off ;-))
That part is awfully close to the exhaust... did you check if the temperatures are within the glass transition temperature of the resin?