I used AKAIO 1.8.9z to update my Acekard 2i to 1.4.4 using a DSi XL which had firmware 1.4.3, and it worked just fine
Maybe its because I didnt place the update file in the root of the microSD card? I put it inside a folder called 'APPS'. Oh and I also used the latest AKAIO loaders:-
These are more up to date than the loaders included with AKAIO 1.8.9z.