I just downloaded the new gog.com downloader 0.9.0.1372 and removed my old adobe air based downloader.
I tried to download a game I just bought with it, but when I click on "add to GOG.com Downloader" in "My account", it doesn't appear in the downloader (this step worked without problems in the old version). I tested this with several games, just in case it was only a problem with the game I just bought, but it always delivered the same negative result.
I restarted the downloader several times, logged in a couple of times and tried it with admin privileges (I'm on Windows 7 x64). So far nothing helped.
Has someone else experienced a similar problem? Any tips?
This same problem kept occurring to me a few days ago. What I finally did to get it working was to go into the options/preferences menu of my browser (I'm using Firefox 4), click on the Applications tab, and find the gogdownloader under the "Content Type" heading, then under "Action" next to it, manually find the place where you unzipped the new downloader and make sure that it is selected. I think that GOG was trying to open game downloads with the old Air downloader (which no longer existed on my computer). I also went into my computer's firewall settings and deleted the old rule that applied to the Air downloader and manually added a new rule to allow the current downloader. That solved the problem for me (at least for most game downloads, I'm still having problems pre-downloading the Witcher 2).
I'm hoping that solves it for you. I'm not a very technical person, but our problems sounded very similar.
(I forgot to add, I'm also using Windows 7 x64).