It could be that the smaller bolt rope is getting wedged in the luff groove. A lot of batten tension can also cause a lot of resistance as could dirt and crud in your mast groove (especially if you've ever used a lubricant.

I would clean the mast groove first using a wooden dowl with a screw in the side of it. Glue some fine scotch-brite to the down and run it up and down the mast groove in the mast by holding the screw. If you get a lot of dirt, use water to clean thuroughly. Then, wrap a wood dowel with cloth (paper towel, scrap rag piece, etc.) and soak the cloth with McLube Sailkote (a dry lubricant that doesn't remain wet or greasy and won't attract grime after it dries). Run the wood dowl/rag combo up and down the luff groove while keeping it soaked with the sailkote. Then spray the bolt rope on the main with sailkote and things should get a lot better.

Another thing that will fight your sail hoist, is an oversized halyard or a halyard with a lot of grip. Because the mast and sail are curved, tension on the halyard tends to bind with the bolt rope of the sail being hoisted. It doesn't sound like this is the direct problem in your case, but the halyard may be pressing the smaller bolt rope into the opening of the mast and causing a wedging action.

If all else fails, I would hoist the sail to the point where it gets stuck and then tip the boat over on it's side (using pads for the hull - lifejackets, etc.). Then take a first hand look at what's going on up there.