OK will take a look at my AV settings. I thought I had excluded all of my FSX folders. thanks.
That's not enough, the antivirus might not block something IN FSX but, it's maybe trying to block the download *from* the FSDT site, and it might also block files as soon as they are downloaded but *before* being copied in the the FSX folder, when they are still in the Windows TEMP folder which was created by the installer.
That's why, if the antivirus it's a problem, it's not enough to exclude files from scanning, even the entire FSX folder, that will only help when you are *running* FSX, but the only safe way to deal with the antivirus when *installing* something, is to turn it off.
This is one possible cause. Another possible cause is that one of the two mirrors we use might be down or just too overloaded with requests (that's why there are two of them running in parallel) and, since they are chosen at random when the installer starts, you might just need to try it again a couple of times, until you'll eventually hit the "good" server.
Again, this is not a problem if you *just* downloaded the Stand-Alone Addon Manager, because the files included in the installer are the same of those that were supposed to be downloaded. In this case, just press the "Next" button, when prompted to "Press the Next button to use Local files".