As Tyson has indicated, we're working on adding some additional redundancy to the DNS for the fatfreecartpro.com domain, on the theory that for some reason it's being flaky or unreachable from certain networks.
However, we currently have no real visibility into what you're reporting--that is, we have not been able to reproduce the problem even once ourselves, which makes it hard to be sure what we're doing will help.
It would help us out if you could file tickets with support with supporting info for this issue--transaction IDs, times your clients were trying to download, what ISP they are trying to download from, what browser they use, the exact error message they got... I realize you probably won't have most of that, but whatever you can give us. Support will round these up for us (dev) and hopefully we can find a pattern here and a way to work around whatever the problem is.
If any of you has this problem repeatably from your own network and could provide us a way to proxy through it to test ourselves (SOCKS4/5, ssh server, VPN tunnel, anything really) that would be most useful.