Instructions
Download the latest version of WAD Manager. Every so often the creators release a new version to add new features or to patch bugs from previous versions. This is especially true if you have a newer WAD to install.
Re-download WAD Manager. You may have corrupted the file or downloaded an older version that is buggy. Make sure WAD Manager is completely downloaded and up-to-date.
Use supported media. When installing applications to the Wii, use an SD card from 1 GB to 2 GB. SDHC is not recommended, especially if you have an older Wii.
Place the WAD application itself on your card in the directory "Apps/WAD Manager" and name the file inside "boot.dol" to ensure it runs when you launch it from the Homebrew Channel.