The most common error for this issue is the fact that the installer placed the plug-in file to another folder instead of the plugins one. Uninstall the product and then install it again and manually select the plugins folder. Make sure that Winamp is closed while this operation is performed. If you don't have the possibility to select the folder, simply let it install in the default folder then manually browse to that folder and copy the files to the Winamp's plugin folder.
