well, it happens here when i use rs, uploaded, netload, ff, megaupload...
no matter what hosts or how many i download from at once, this error occurs every 2nd day or so out of the sudden.
all running downloads are failing then and set to the described error-message + they are disabled.
i have always using 1 chunk only and never used the unrar plugin, so i can trace it to the level, that those, like some people assumed in this thread, are not the cause of the problem.