Roller furling main locks when reefing
Put a bit more tension on the outhaul. Raise the boom a bit above horizontal when reefing or furling and check the luff and furler tension. I have only one season experience with a Sparcraft furling main but have not experienced this problem. In fact it has performed flawlessly. The only time something similar happened was when I mistakenly tried to furl the main without fist releasing the furler line.