I'm not sure if this is your case or not, but if you try to up-load a sketch to a chip with a Uno bootlader on it and you choose Duemilanove as the board, you will get the sync error, and vice-versa. Are you sure which bootloader each of the Freetronics boards has? Freetronics claims that both boards should be treated as Unos. Is there any chance the bootloaders got changed?