I agree with Don about it probably being a mixing problem. If you can apply heat you might even get a mis-mixed batch to cure.

This reminds me of a class I took with Chris Kulczycki at Wooden Boat School. On the first day we all unpacked our Cape Charles kits and set to work. We cut scarf joints in the Okoume plywood and the sheer clamps. Towards the end of the day we glued the scarfed joints in the plywood together and glued the sheer clamps to the ply and glued their scarf joints at the same time. (You can imagine how many clamps this takes when you're building 7 boats at a time!)

The next morning we went back to the shop and took off the clamps. We were working in teams of two people to help handle the long panels. My partner took his clamps off and everything oozed apart. Chris K came over and took a look. He clamped everything back together and tried giving it some more time and heat. By lunchtime the epoxy was still very soft.

The funny thing (well, not so funny for my partner) was that we both remembered the exact momment that my partner had mixed up this batch of epoxy. We were standing together in the doorway and he asked me what the proper ratio of hardner to resin was. In spite of checking, something still went wrong.

We only had a carefully orchestrated week to build these boats and all morning, while the rest of us were wiring our hull panels together in the shape of kayaks, my partner was sitting there watching epoxy not cure.

THE SOLUTION After lunch we ripped everything apart. Since the sheer clamps were just pine we threw them out and cut new ones. My partner cleaned the uncured epoxy off the more expensive Okoume plywood with acetone. We glued everything back up with a fast hardner/resin mix. By the time we left for dinner it was clear that the epoxy was setting up alright this time. By the end of the week we had rushed his boat along enough so that it was finished on schedule with everyone else's.