I was a "backer" and have just downloaded from GOG without any problems
However, I discovered that there wasn't a Part One and a Part Two as I had expected - just the whole
"Broken Sword 5" game.
For me that was straight forward because I had waited until the whole game was available before I downloaded anything.BUT
I can understand the frustrations of those who downloaded Part One when IT
was made available because, apart from at the forum related to the game, I couldn't find any information as to why only the whole
game is now being offered as a download.
And at the forum there are a lot of people venting their displeasure about that !! EDIT
I just went back to GOG and the advice at the forum appears to be to back up any saves from a previous play of Part One, then uninstall
that Part One and download the full game
that's now being offered.
Apparently quite a lot of technical changes have been made and that is why only the full game download is now available.
It does sound, though, as if saves made during the that original Part One will work with this new full game download.
[There are six "items" to download but with superfast Broadband the whole thing took less than hour for me.]