update manager wont update

when i try to update my computer i get:

could not refresh the list of packages

ERROR###ERROR###ERROR###ERROR###ERROR###ERROR###ERROR
W:Failed to fetch gzip:/var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_quantal_universe_binary-amd64_Packages Hash Sum mismatch
, W:Failed to fetch gzip:/var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_quantal_universe_binary-i386_Packages Hash Sum mismatch
, E:Some index files failed to download. They have been ignored, or old ones used instead.

I also got this message with the error:

"The repository may no longer be available or could not be contacted because of network problems. If available an older version of the failed index will be used. Otherwise the repository will be ignored. Check your network connection and ensure the repository address in the preferences is correct."

i can go on the internet and watch vidoes fine, although i do sometimes have to turn my wireless receiver off then on to get the internet working again.