i have 12.04 LTS but i have a strange problem from a while
every time i try to do an update an error window apears with "check your internet connection"
and i have tried to update file by file which was boring and very not exciting
finally I found 4 files those was the problem
libproxy1 (size: 57kB) libproxy1-plugin-gsettings (size : 22kB) libproxy1-plugin-networkmanager (size :7kB) python-libproxy (size:5kB)
by the way i tries to change the server and this problem still the same please give a way to end this problem because every time i need to update i have to look for those files and excludes them from the update .... try to look for them into 170 files (I did)