No, re-adding the source does not fix the key problems.
Under 10.1 the pubkeys are discovered automatically, but often packages do not have their sigs adjusted.
For 10.1 all you have to do is "update" the source to pick up any changes.
For 10.0 and before you must manually add the keys...
Add the sources as indicated above, and then to update your ENTIRE system at once type in
in a root console.