Getting a 404 error reading CRAN mirror repository

Dear all,

I try to get a CRAN mirror repository working on my Ubuntu trusty 
plateform. So, including e.g.:

deb https://mirror.ibcp.fr/pub/CRAN/bin/linux/ubuntu trusty universe

in /etc/apt/source.lst

However, on every mirror tried I get:

Err https://mirror.ibcp.fr trusty/universe amd64 Packages
   HttpError404
Err https://mirror.ibcp.fr trusty/universe i386 Packages
   HttpError404

Can someone figure out what is going wrong ?

Best,

Patrick