Corrupt rars on every file

Ok so ive grabbed the bluray copy of black hawk down on nearly every server now and always getting corrupt rars. Not enough blocks to repair with as ive checked, buuuut the file size on the site compared to the file size grabbed by me is different so obviously im not grabbing all for some reason. I use grabit and i was wondering if there is any way i can redownload the file whilst checking the files i already have thus skipping the these and redownloading the files i am missing? any info grearly appreciated.

EDIT

I am using thundernews.

If Grabit won't show you meaningful error messages, use a newsreader that does.

Yeah grabit is shit IMO....use Newsleecher, SABNZbd, Alt.binz, NewsBin Pro or the like.