It means that the other hosts have a different version of the file you are requesting. There is an overlap when doing multy part downloads and XoloX checks for data integrity. When the recieved partial doesn't match it will be dropped. If this happens an x amount of time XoloX will go to safe mode.
All this means is that it will try to download the remaining part of the file from the last reliable host (eq. the last host that gave you correct partials).
Hope that explains.