How to revert software sources back to default? [duplicate]

Question

Possible Duplicate:
How do I fix this “E:Type '*' is not known on line * in source list …” update error?

I had a little problem with the sources of my update, I'm running Ubuntu Natty Narwhal and I was tinkering with binaries for installing a Firefox add-on called fire sheep and I think that some how my update sources were altered and evertime I try to upate I get this error message

An unresolvable problem occurred while initializing the package information.

Please report this bug against the 'update-manager' package and include the following error message:

'E:Type 'See' is not known on line 2 in source list /etc/apt/sources.list'

Answer 1

I don't think it has anything to do with the add-on but I had a similar problem. Somehow your sources.list is modified on line 2. Do this:

Make a copy of your sources.list, just in case you need to revert the changes:

sudo cp /etc/apt/sources.list /etc/apt/sources.list_backup

Open the file with an editor, like:

gksu gedit /etc/apt/sources.list

In the second line you'll find the problem: That sentence:

See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to

has to be commented, otherwise the update manager will try to read it as a source and that's the error you are seing.

Simply add a # in front of that line. I should appear like this:

# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to

If the problem persist, maybe because you have other lines with the same error, just correct'em all. But DON'T comment all the lines, first try to find which ones are wrong. Run update-manager each time and if there's an error it will tell you the line where it is.

Good luck!