Thomas, I just want to thank you for posting this note about your resolution. You never know when a seemingly minor thing makes a major difference to someone else! I have been struggling with the same "Hyperkitty failure on..." error message for days, and while I made sure, with copy/paste, again and again, that the api_key string matched the SECRET_ARCHIVER_KEY string, I was still using the string that came with the Django local settings file on install (32 character string of random characters).
I just changed the key (in both places) to something new and simple for testing and magically my archives are working! In fact every test message I've sent since initial setup is there (where were all those durn things hiding anyway???). I don't know if one of the characters in the original string is a no-no in Ubuntu, or if a non-printing character was hiding in there, or WHAT, but...
It works! It works!!
Thanks Mark S. as well for your help finding the logs and getting me pointed in the right direction.
Now that I've done it, turns out installing MM3 on Ubuntu 8.04 using the mailman3-full distro (w/ apache2, postgresql, postfix) is a VERY simple and straightforward process with relatively few steps (just a couple really critical, non-obvious ones!). I'll post a walkthru once I've tidied it up a bit.
~Kelly