How did you manage to downgrade to 8.0 with a Samsung ATIV S I also own? I read some decriptions of downgrading and all mentionned Nokia Software Upgrader as the tool used. I cannot imagine it will also work with Samsung devices.
I have a Samsung Ativ S, and had the 80188308 error even after i reset my phone. Now i made it, i have updated my phone (i had to downgrade to wp8.0 and then update 5-6 time until i get all updates). My ROM is GT-I8750_XXCMK2_R_signed, and my CSC is COA (i had the same even before downgrade so i dont know what the problem was)
Sorry for my english...