I got a reboot loop after doing the last KP thumb, no big deal, cant use backupmenu with the new kernel(damn I wish backupmenu could work to back-flash a kernel too!).
So I cable reflashed with RX-51_2009SE_20.2010.36-2_PR_COMBINED_MR0_ARM.bin and when I try to load the backup the recently working repos all come back invalid. Is this the SSL issue or are repos down?
I have not had to do a cable flash since before Maemo spun off from Nokia.
Even disabling the working a few weeks ago repos and clicking on the TMO CSSU testing install link shows a broken repo.
My google-fu is failing me on finding the right thread.
I want to get back kernel power and CSSU thumb asap as this is my everyday phone.
At this point I cant even get sudo or ssh installed.

I remember at one point there were instructions to build a flashable image from a backupmenu archive, that would work for me too if I had how to determine which and where to find the correct kernel.

What repos are you refering to?
Those?
Then I do not get what kind of problems you have.

Did you set the phone's date and time accordingly?

I had not, but it self updated via the carrier...
still not working
Those two repos(and BME repo) are the only to update, so I can install a total of six debs, including Amazon, AP News, and Forecast weather.
Extras, and extras testing and dev are no good as well as CSSU and thumb

I am currently getting most of what I need through the CSSU-thumb repo, nothing else(except as above) is responding.

I was able to get enough installed through CSSU-thumb repo to bootstrap Backupmenu into working.
Back to normal for my N900, though most repos still not responding.

The muarf.org mirrors, that @peterleinchen pointed you to are working fine here.
They are just producing the same old warning about the expired repository keys.

Wasn't CSSU supposed to fix the keys?

Which repos are not working?

Normal repository.maemo.org ones?
They are working fine for "all of us". At least no on else complained (including me ).

Or the old maemo.nokia.com ones, which are now mirrored?

I read that the maemo.org are affected on your device.
Did you try to ping them, browse via http? It seems to like a DNS or network problem on your side?
Did you check the settings? Or /etc/apt/sources.list.d/hildon-applica
tion-manager.list?

I have been pinched for time, even more so with the reload. I have been adding repos and doing the reload while walking down halls or catching buses. Once I have time to diagnose I will post results and any fixes. It is interesting as the repos do not respond either under home wifi or via 3G internet connection. They are the current laptop verified up repos as I deleted the ones I had and re-added them from the just verified http://repository.maemo.org
Strangely the problem remained even after I was able to do a backupmanager system reload.