If you've already upgraded your Wii to the official 3.4u or 3.3u firmware, then you'll need to downgrade it before the backup loader can work. Everything you need to downgrade your firmware from 3.4u or 3.3u (or any other region 3.3e etc) is included in the 002fixGammaLoader.zip file. Also, to downgrade the Wii firmware, you will need the Wii connected via Wifi so that it can download the firmware that you select.

Steps to downgrade your Wii firmware:

• Load the Homebrew Channel
• Navigate to the "C. Custom IOS Downgrade", press A
• Once the Downgrader boots, select the firmware you'd like to downgrade to. I suggest 3.2U (for USA ONLY!)
  Remember to only pick the firmware for your region Wii. For example, if you own a USA Wii, the pick any firmware ending in "U" like 3.2U. If you own a European Wii, then select the 3.2E etc..
• follow the on-screen instructions and within 10-15 minutes, your Wii will be back to whatever firmware you selected. This thing works great!