Comment 2 for bug 1371942

Additionally, the Settings button leads to a Tab in Settings where there's nothing related to trusted/untrusted packages.
Ther relevant tab is Authentication, but you have no clue of what you are supposed to do there, because
- the error message didn't tell anything about what are the problematic untrusted sources that allegedly are required
- there's no option to "allow untrusted sources" or anything like that, so you should magically know which source you would need to add

And most important, Update Manager should at the very least let you install ALL OTHER updates except the ones that are causing the issue, so at least one would be able to isolate them.

Altogether this is designed in the worst conceivable way.