Why is this happening .
I used pro finish carbon
Sprayed the mold with the gc50
Left over night to cure !!!
what can I do to rectify the delaminaton problem

The only times I've ever experienced any de-lamination issues with GC50 is either when it or the epoxy has cured in quite cold conditions (i.e. if left overnight in a garage) or if I might have used a little too much spray tack during lay-up. This has usually been is quite localised areas, though

I often leave the coating to cure overnight, but use a 'hot box' now to maintain a decent temperature. Not certain if either of these scenarios might have affected your bond, but I've found it to be very reliable if curing of both the coating and the epoxy is done at reasonable temperatures (not below 15 degrees, at least)