curl:(22)The requested URL returned error: 404 Not Found Trying a mirror...==>Downloading ftp://ftp.simplesystems.org/pub/libpng/png/src/libpng16/libpng-1.6.17.tar.xz curl:(78)RETR response: 550 Error: Failed to download resource"libpng"Download failed: ftp://ftp.simplesystems.org/pub...