Well I've been using the GoG down loader and haven't had any problems until today.
I kept getting a message that said all D/Ls had to be stopped and it displayed [E1003} on it as well.
I couldn't figure out what it was but when I deleted the game at the top of the que (Settlers 2 Gold) it worked again.
I tried putting it back on and I get the same error message but now it displays [E1004]
Any ideas on what's going on?

Nevermind, Thiev already answered the question ;)

well it happened with Castles too, but I removed both of them and it seems to be working now, I'll try later to see if those 2 games work then if not I'll be back haha