Hi!
I'm afraid there are some problems with your HTTP and FTP services for both centos and centos-altarch:
http://ftp.rz.uni-frankfurt.de/pub/mirrors/centos/TIME => HTTP 403 Forbidden
ftp://ftp.rz.uni-frankfurt.de/pub/mirrors/centos/TIME => Could not chdir to mirrors: server said: mirrors: No such file or directory
I think these should be fixed.
It shows that one should check that the new config is active before submitting.
Should work now.
Best regards,
Sven Specker