Still working on a a Joomla website 1.5 with Autotweet 4.12 (Joomla will be updated in the fall) I tried the workaround for a Twitter channel.
I installed AutoTweet on a test site, created the app incl. read&write application type, generated the tokens en validated them on the testsite (succes).
Then copied the tokens to the J1.5 site, saved the channel.
After this, the channel gives a 401