[xubuntu] Upgrade ubuntu from 11.4 to 11.10

Hi Experts

I running Ubuntu 11.04 on Mac using Virtual box and trying to upgrade Ubuntu 10 11.10 by going to system-->Administration-->update manger

but keep getting the following errors during the upgrade , can you please advise how can I solve this issue

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"Error during update

A problem occurred during the update. This is usually some sort of network problem, please check your network connection and retry."

W:Failed to fetch gzip:/var/lib/apt/lists/partial/security.ubuntu.com_ubuntu_dists_oneiric-security_multiverse_source_Sources Hash Sum mismatch
, W:Failed to fetch gzip:/var/lib/apt/lists/partial/security.ubuntu.com_ubuntu_dists_oneiric-security_universe_source_Sources Hash Sum mismatch
, W:Failed to fetch gzip:/var/lib/apt/lists/partial/security.ubuntu.com_ubuntu_dists_oneiric-security_restricted_binary-i386_Packages Hash Sum mismatch
, W:Failed to fetch gzip:/var/lib/apt/lists/partial/security.ubuntu.com_ubuntu_dists_oneiric-security_multiverse_binary-i386_Packages Hash Sum mismatch
, W:Failed to fetch gzip:/var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_oneiric_restric ted_source_Sources Hash Sum mismatch
, W:Failed to fetch gzip:/var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_oneiric_restric ted_binary-i386_Packages Hash Sum mismatch
, W:Failed to fetch http://us.archive.ubuntu.com/ubuntu/...ted/i18n/Index
, W:Failed to fetch gzip:/var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_oneiric-updates_restricted_source_Sources Hash Sum mismatch
, W:Failed to fetch gzip:/var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_oneiric-updates_multiverse_source_Sources Hash Sum mismatch
, W:Failed to fetch gzip:/var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_oneiric-updates_restricted_binary-i386_Packages Hash Sum mismatch
, W:Failed to fetch gzip:/var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_oneiric-updates_multiverse_binary-i386_Packages Hash Sum mismatch
, E:Some index files failed to download. They have been ignored, or old ones used instead.

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Regards
Fadi