(Prescript: I have to ask. Is there some reason why you’re keeping three-hundred-odd completed tasks in your task list? You don’t need to. If you right-click on them and remove just the task, the downloaded files will remain, and this will unclutter your task list.)
It’s up to you to determine why BitComet can’t write to the disk, and to solve the problem. BitComet, like all programs, foolishly relies on the system to inform you of system problems. (After all, the system doesn’t tell IT why, either. It just throws “disk write call failed”.)
The first place to look is, always, the system error log, to see how it may enlighten you.
Write a little nonsense text file in Notepad and save it to your default download directory. Can YOU write to the disk and to that directory?
BitComet has a setting which, by default, preallocates the entire amount of disk space that the file will consume when it’s finished. This is done because the pieces you get do not come in any particular order. The first one you get might be piece number 32,565 out of 100,000. If you carefully manage your disk space, you can turn this preallocation off, which will give you some time to move things around, burn to optical disk, make room for the file as it is downloading.
But if you have preallocation turned on, and you’ve started several tasks already, they will all preallocate all of their needed disk space, or try to. If there’s not enough room, then they’ll stop with the “can’t write” error because all of the disk space is reserved, even if it’s not actually taken yet. Try freeing up more disk space, then stopping all of the tasks, deleting (task & all files) all but one . Restart that one task. If it picks up and rolls along now, that was your problem. Turning preallocation off just postpones, does not solve, the disk space problem. If you usually run with so little free disk space, this problem will become an old friend. Burn a bunch of stuff to DVD, or get another disk drive, they’re very cheap now.
If that doesn’t work, you can try stopping the task, deleting it, re-adding it using the file menu (not drag&drop), then change the download location for this task to another path, ideally another disk, something simple, something you know exists because you just created it, viz, “E:\NewDirIJustMade”, then start the task and see what happens. Even if it doesn’t work, it still tells you something.