Sometimes a file named fst.bin.xxx (a temporary file) is stuck and preventing the real fst.bin from being updated. Navigate to your user directory: Dolphin Emulator/Wii/ . Locate and delete any files ending in .xxx .
If you see "dolphin iosfs failed to write new fst," your emulator cannot save data to your hard drive. If that fails, resetting the Wii folder (Method 4) will force a clean slate. dolphin iosfs failed to write new fst