Hi newbee2
Long time no see (or should that be "read/write")
Anyway, to answer you question (and when I used to use LW), I believe that when your download reaches 100% LW copies the file over to your "Complete" folder then deletes the original that was the "Incomplete" folder.
I also believe that when LW gives out a "Disk Error" it is caused because LW cannot "see" enough disk space to make its copy in the "Complete" folder.
Please note, the above is just my observations.
Glad to see you around the forum again.
UK Bob