I am currently using similar resist I got on eBay.
I have not yet had problems with it flaking off.
I follow a procedure much the same as James detailed.
However... to test some exposure times I laminated a scrap bit to an old piece of board. The board was dirty and after testing I left it lying around... the sunlight baked the resist very well after a few days.. the whole lot flaked off easily after that.
So maybe your board is not clean enough or you have some solvent residue or such or you are over-exposing.
I have not yet had problems with it flaking off.
I follow a procedure much the same as James detailed.
However... to test some exposure times I laminated a scrap bit to an old piece of board. The board was dirty and after testing I left it lying around... the sunlight baked the resist very well after a few days.. the whole lot flaked off easily after that.
So maybe your board is not clean enough or you have some solvent residue or such or you are over-exposing.