package exim4-config 4.69-2ubuntu0.3 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1

 it is showing the folllowing message every time i am writing the commmand sudo ato get update ......Failed to fetch http://in.archive.ubuntu.com/ubuntu/dists/hardy-backports/Release Unable to find expected entry 'multiverse\/binary-i386/Packages' in Release file (Wrong sources.list entry or malformed file)

E: Some index files failed to download. They have been ignored, or old ones used instead.

first it starts the update but at the last moment this message comes and the update is not completed ........ please tell me some commands that i can use to to remove it .......

ProblemType: Package
DistroRelease: Ubuntu 11.04
Package: exim4-config 4.69-2ubuntu0.3
ProcVersionSignature: Ubuntu 2.6.38-8.42-generic 2.6.38.2
Uname: Linux 2.6.38-8-generic i686
NonfreeKernelModules: wl
Architecture: i386
Date: Wed Aug 31 10:16:02 2011
ErrorMessage: subprocess installed post-installation script returned error exit status 1
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release i386 (20110427.1)
PackageArchitecture: all
SourcePackage: exim4
Title: package exim4-config 4.69-2ubuntu0.3 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1
UpgradeStatus: No upgrade log present (probably fresh install)