Might be this, switch your antivirus off, and see if the problem goes away
If it does its because its scanning the zip for its contents before its downloaded, and this is causing some type of backwards and forwards lockup (likey everytime the file adjusts in size (as it downloads) the antivirus rescans it), if this is the case you can normally set anti virus programs to not scan a certian folder, then download your zips to that same folder, and either move them out of it, causingt he antivirus to scan them or manually scan them once downloaded.
