Torrents are downloaded to your computer piece by piece. Once complete, the pieces form a whole, but that is never achieved if the download never completes. Torrents that are stuck at 99 per cent completion can be extremely frustrating, as some can take days to download to that point and then not complete. One cause for this problem is when the final pieces of the torrent are simply not available.
Wait a couple of days and check again. Torrents are downloaded piece by piece from other peers. If the torrent you are downloading doesn't have many seeds, it will be harder to find someone that has the last 1 per cent that you need. Leave the application running overnight or longer, if necessary, to let it finish downloading.
Turn off DMZ mode from your router's set-up page. Turning this option on can mangle the last packet of information, which may cause the download to fail hash checking. Hash checking is a way for your peer-to-peer software to confirm that the file you're downloading matches the original. If the hash checking fails, the last piece of the file never downloads.
Connect your computer directly to the Internet, bypassing the router completely. This takes the router out of the equation and eliminates the hash checking problem. If your router is built into your modem, enable bridge mode from the "Network and Sharing Center." Click the "Change Adapter Settings" link, right-click your connection and choose "Bridge Connections." Make sure that your Windows firewall is enabled and your operating system is fully patched through Windows Update. Type "Firewall" in the "Start" menu and click "Check Firewall Status." All networks should be green, not red, and show "On" for the firewall status.
You might just have a bad torrent that is not 100 per cent complete. Open your file sharing program and look under "Seeds" to see how many people have the complete file. Go back to the site where you found the torrent, and copy the hash from the page. Paste the hash into Google to search for additional copies of the torrent.