This was happening to me on my BR-1600. I optimized the song, deleted unnecessary tracks, re-optimized and it kept happening. Anytime I tried to record another track it would stop in the middle with "Drive Busy!". It drove me nuts. I did a search on the Roland site and came up with the recommendation to initialize the HD. It recommends doing this every two to three months depending on how much you use your unit.
I backed up all my stuff to my pc, initialized the drive (a step called surface scan) which wipes everything clean, moved everything back and yeah! Problem fixed. I was relieved because I was starting to suspect I had a slowly-failing HD.
I know it's not the 2400 but I would suspect it could be the same issue of fragged data.
NV