Thanks - I'll have a go at upping the Java limit, but I've had a breakthrough. I've had the same issue occur a few times while subsonic has been stopped, but I've been copying the music in bulk to another computer.
I now suspect disk integrity, which goes some way to explaining the symptom. I've run chkdsk with no reported errors, but that didn't seem to check too deep. The drive is a software mirror across two physical disks.
The issue doesn't seem to be related to any particular files - retrying after a fail will result in a successful copy. I guess this could be luck though if one of the physical disks is dodgy.
