Judging from your info:
a) you had a working v8.560 nc of bl equal to 5.5229 on your external 8GB SD card.
b) you made a nc v9.000 installation on the 8GB card, but it does not boot; the new bl was flashed into the device.
c) however, the internal card (2GB) is still booting (the official nc) and there is a new bootloader 5.5256 on device.
If a+b+c are true, then the new bl 5.5256 (that came with nc v9.000) does not support 8GB cards.
Fortunately, you can go back to a bl supporting 8GB cards, with dsa.exe.
The recipe is in post #10
(you may do an extra test first: back-up your internal card and install on it nc v9.000; it should boot from there)