Thanks for your answer dirk! 
I've tried a few different mirrors before, including the rstudio one. To be sure i've tried again with the one you provided, but didn't work.
I've found this other method, that worked. I guess it's not the official one, right?
sudo add-apt-repository ppa:marutter/rrutter 
sudo apt-get update 
sudo apt-get upgrade 
from the following SO answer.http://stackoverflow.com/questions/15260250/re-installing-r-linux-ubuntu-unmet-dependencies-r
Martin

> Date: Fri, 18 Apr 2014 06:58:36 -0500
> To: edd@debian.org
> CC: belmartin@outlook.com; r-sig-debian@r-project.org
> Subject: Re: [R-sig-Debian] Ubuntu 13.10 - not able to upgrade R
> From: edd@debian.org
> 
> 
> On 18 April 2014 at 06:01, Dirk Eddelbuettel wrote:
> | You have a network error with the host, so use a different mirror.  I use
> | 
> |     deb http://cran.rstudio.com.org/bin/linux/ubuntu saucy/
> |  
> | as I found the RStudio CDN to be reliably fast.
> 
> That's what I get for editing on the fly.  URL should be 
> 
>      deb http://cran.rstudio.com/bin/linux/ubuntu saucy/
> 
> I am trying to switch more machines from using r-project.org to rstudio.com
> which serves faster...
> 
> Dirk
>  
> | Dirk
> | 
> | | I've done this a few times. At this point there are no more updates and the R error is isolated.
> | | Is there a solution to this or should i just re-install R.
> | | Thanks for your time,
> | | Martin
> | |  		 	   		   		 	   		  
> | | 	[[alternative HTML version deleted]]
> | | 
> | | _______________________________________________
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> | 
> | -- 
> | Dirk Eddelbuettel | edd@debian.org | http://dirk.eddelbuettel.com
> | 
> | _______________________________________________
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> | R-SIG-Debian@r-project.org
> | https://stat.ethz.ch/mailman/listinfo/r-sig-debian
> 
> -- 
> Dirk Eddelbuettel | edd@debian.org | http://dirk.eddelbuettel.com
 		 	   		  
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