Two Parter. Why bad newsgroup downloads? Mass .par checker?

Hey guys, two part question. I'm kinda a download addict from newsgroups and for some reason I always get downloads that need to be repaired via .par files, its not really a problem, just takes longer of course. Is there anything I can do to stop this problem? I'm using giganews which I get amazing speed from, and I'm using newsbin pro registered. I'm also using newzbin to get the file lists if that matters. Anything I can do?

Second part, Like I said, I have to repair alot and I currently have about 300 gigs of downloads to sort thru and repair if needed, is there any program out there that will do it in mass? I have a mass un-rarer and it works great, I guess I'm looking for the same thing in .par format. Any suggestions?