i cant download from ubuntu software center

[charbel obeid]

when i try to download any application from software center after asking me to put my password it give me this two messages
1- "failed to download package files. check your internet connection"
i cheked my internet connection and it's working and i can browse sites using firefox without any problem

2- " requires installation of untrusted packages. the action require the installation of packages from not authenticated sources.

i am using ubuntu 11.10 and software center 5.0.4

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: software-center 5.0.4
ProcVersionSignature: Ubuntu 3.0.0-16.28-generic 3.0.17
Uname: Linux 3.0.0-16-generic i686
NonfreeKernelModules: wl fglrx
ApportVersion: 1.23-0ubuntu4
Architecture: i386
Date: Mon Feb 27 15:14:46 2012
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release i386 (20110427.1)
PackageArchitecture: all
SourcePackage: software-center
UpgradeStatus: Upgraded to oneiric on 2011-12-20 (69 days ago)

[Gary Lasker (gary-lasker)]

Hi charbel, and thank you for your report. This appears to be a duplicate of bug 986929, so I am marking it as such. Please check that bug for further information about this problem, and for advice for how to resolve problems of this type.

Thank you again for your help!