The most common issue we see with complaints of large files recently downloaded from another source (usually sound sets) is because the data connection used to download the file is not a broadband connection, using any wireless technologies like AT&T U-Verse, or your phone as a hot spot can corrupt the download as it will lose data during the transmission process. Even using a slow wireless router at a coffee shop where the bandwidth is limited can cause this.
You need to be on a hardwired connection into your router / cable modem for these downloads. You want to be attached to a Cable Modem, FiOS, Google Fiber, DSL, anything with a hard line attached to the computer.
I imagine these stem downloads are massive as a single file. Try downloading them 1 at a time. You may want consider using a download manager like "Internet Download Manager" or something like it that creates multiple connections to bring your file down more efficiently and all in one piece.
I've asked the contact for Dueling Mixes to offer additional answers here.
