Found the issue, seems like debian mirros have changed in the meanwhile.
The following commit fixes it:

commit c079993074e197f57065e1eee7764696d446df38
Author: Khem Raj <raj.khem@gmail.com>
Date:   Fri May 4 14:56:33 2012 -0700

     classes/mirrors.bbclass: Point snapshot.debian.org mirror to 
working location

     If you point to snapshot.debian.net/archive/pool then it will fetch
     you a html page which will end up in corrupt download. The locations
     have changed for archives and here we point the mirror to right
     location.

     (From OE-Core rev: 15e8aa4cd773022b36a66f70e4f6436289f3d1bc)

     Signed-off-by: Khem Raj <raj.khem@gmail.com>
     Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>



Richard, do you think you can push it into the denzil branch?
Thanks


>
> On Wed, May 23, 2012 at 12:04 PM, Foinel <flocirel@gmail.com 
> <mailto:flocirel@gmail.com>> wrote:
>
>     Hello,
>     I'm trying to use the denzil branch and encounter some issues with a
>     package. netbase to be more precise. On upstream, netbase 4.47 does
>     not exist anymore. So it automatically tries a mirror to download
>     netbase 4.47. It ends up fetching the package from
>     http://snapshot.debian.net/archive/pool/n/netbase/netbase_4.47.tar.gz
>     . The package from this mirror seems broken though and do_unpack fails
>     with "gzip: stdin: not in gzip format"
>     Now my question is: why doesn't it uses
>     http://downloads.yoctoproject.org/mirror/sources/ ? Which is the
>     scenario when it fetches from the yoctoproject mirror?
>
>     Thanks.
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>
>