I have a similar problem, in my case it is caused by having satellite internet rather than DSL. Essentially the satellite signal is intermittent and the file software thjinks you're logging on 100s of time a second and want's you to slow down and stay connected . . . which is not possible witgh a satellite internet link. DSL isn't available in my area so the only way I can downlaod from BRP central is if I take a laptop & go to someplace that lets me hook up via DSL or use WiFi that links thru DSL, my home computer is just out-of-luck.
Not sure if that's you're problem, but if you have satellite internet it probably is. Unfortunately the only solution I've found is log on and download from a better location.
I get the same trouble with alot of internet downloads like from DriveThruRPG and Paizo, but apparently Amazon's file download software isn't phazed the intermittent nature of satellite internet, so it varies.