Which game are you having issues with?

It'd best to NOT use a proxy as that's what's messing with your downloads :)

Or you can configure it to let the downloads through but I am no expert on proxies and always found them to be a pain in regions one does not discuss in polite company :)

The downloader is NOT a client, just a downloader for our games. You also have the option to use the downloader unlike clients that are usually forced on you when you want to use some services. You can easily use the Downloader to download your games and then exit out of it and play them without it :)

Using the Downloader is the, arguably, most convenient workaround, but here's how it works:

Our browser download links are (among other things) IP-sensitive, to accommodate browser download resuming while remaining secure.

This works under normal circumstances, but, unfortunately, we have learned that, in very rare cases, if a user's connection assigns a different IP when connecting to our site, and then a different IP when the actual download is initiated with our file hosting provider, an IP mismatch occurs, resulting in the 403 error. We are currently unable to resolve this issue, whilst preserving our users' ability to resume browser downloads.

If you've set up a proxy connection yourself, you should make sure that the same proxy is used for all connections, rather than only some of them.

If all of this happens in your ISP's back-end, it may be possible for your network administrator to modify your network setup so that you are issued the same IPs for both GOG.com, and our file hosting provider's servers, which you eventually get redirected to. Unfortunately I cannot guarantee if this will work, nor if the network administrator would agree to making such a change.

I'm sorry about the inconvenience, but we had to introduce this change in order to facilitate browser download resuming - one of the more popular user requests at the time. This implementation works an all but the most convoluted network connections, and we do have a known workaround for such cases (the Downloader).
Unfortunately at this time the only "fix" for this would be to scrap browser download resuming and do a rollback.

Please note that the Downloader provides considerable benefits such as download corruption prevention, speed throttling, and multiple concurrent downloads to squeeze every bit of transfer speed out of your connection. Downloading and installing the application takes about a minute total, and you can uninstall it once you no longer need it.
I hope that this isn't a considerable inconvenience.

That's harsh, right in the heart.
Why do you think it sucks, what can we improve? :)

Well, I think tinyE might be beyond improvement :P

Just so you know I am kidding :P

Hope you didn't take it the wrong way :)

Oh snap :)