This is a complicated bot to make work regardless of who wrote it. You need to take precautions such as entering the farm before you press start, to make sure: A) no one else is already in there farming, and B) keeping an eye out for people that don't follow the first precaution because they will come in and start planting in your rows.
I always grab seeds, enter farm, set world, and start the bot while standing exactly where it plants the first seed. If you do this and keep an eye out for crashers/idiots, this bot will work flawlessly.