i have answered this in detail earlier too....

in short : there is no real solution as this is not a bug in torrent client but in way OS handles file I/O... 99% we get this error in first or last section of downloaded file.. cauz at times file spans out of the OS sector (4mb)... so when we delete / move adjacent file.. some section of our torrent file looks to be deleted and hence hash fails ...

setting this value in utorrent (advanced) to true helps alot :-

prio_first_last_piece

google ^^ and you can get details...

there should be something similar in other clients also...