Bittorent can't find my files?

[RikuoAmero]

Okay this is a bit of a head-scratcher for me. I've got Bittorent 7.2.1, and as of just last week I've reinstalled Windows, so there really shouldn't be a problem. However, its lately gotten into the habit on some of my torrents to download part of it, then for some reason stop and say it can't find the files. I right click the torrent and click on Force Recheck, but this can take a while on some of my larger torrents (this has happened on a 80gig+ torrent). That does find the files, but why does my computer think it can't find the files its been writing to all day?