I've found out a way to fix the error message "unable to copy datas" On savegame manager GX. I don't know if this will work for everyone but it worked for me on vWii.
Step 1: Select the game/games you want to extract to the SD Card
Step 2: When it says "extract to", press custom
Step 3: Press the folder icon in the top left
Step 4: Press Cancel
Step 5: Press the USB icon in the top left, it should change to an SD Card icon. From there just choose the folder where you want your save data to be extracted to.
I've attached the version of SaveGame Manger GX I used.
Hope this helps!
Step 1: Select the game/games you want to extract to the SD Card
Step 2: When it says "extract to", press custom
Step 3: Press the folder icon in the top left
Step 4: Press Cancel
Step 5: Press the USB icon in the top left, it should change to an SD Card icon. From there just choose the folder where you want your save data to be extracted to.
I've attached the version of SaveGame Manger GX I used.
Hope this helps!