ftp.tu-clausthal.de has no stage tarballs: yafc ftp.tu-clausthal.de:/.../gentoo/releases/x86/2004.3/stages> ls athlon-xp i686 pentium3 pentium4 x86 athlon-xp i686 pentium3 pentium4 x86 yafc ftp.tu-clausthal.de:/.../gentoo/releases/x86/2004.3/stages> cd x86 CWD command successful. yafc ftp.tu-clausthal.de:/.../gentoo/releases/x86/2004.3/stages/x86> ls -l total 0 drw-r--r-- 0 owner group 0 Nov 13 14:40 x86 yafc ftp.tu-clausthal.de:/.../gentoo/releases/x86/2004.3/stages/x86> cd x86 x86: No such file or directory.
Seems that the mirror has been fixed as it now has stage tarballs.