Some rim/tyre combos seem to be particularly hard work, and I always seem to end up buying them.
Due to my experiences I have made a few observations on the subject. The most significant is that you should make sure you use good thin tapes, fat tapes will make this problem a lot worse, as will rim tapes that are too wide. With folding tyres I have found that, when possible, deflating the tyre working it a bit on the rim and then leaving it for a few hours will aid removal.Finally if the well of your rim is deep use a tyre lever to work the bead into the well on the opposite side to where you are starting the removal process.
My final observation is that tolerances in tyre manufacturing are perhaps not as good as they could be as I have had tyres that slipped on and off my rims with no trouble and replaced them with supposedly identical tyres only to find them almost impossible to fit.