i don't think there is any need to step in here and be pro bono attorney, good cop, bad cop, donut-eating cop, protector, white knight or helicopter-parent for otto. i'm assuming otto is a reasonable, grown adult who can respond for himself, if he so chooses. i feel if you upload a plug-in to the wordpress.org repository, for pay or no, you commit yourself to supporting that technology for its lifespan and responding properly when users report valid issues with a bit more than “i need more info, it's working for me,” when plenty of info to reproduce has been detailed. if you do not wish to support your tech, you should remove it from the repository and notify of such where you can.
the quick work around to get out of the trapped hell of not being able to log-in with otto's facebook connect plug-in turned on for your WP site is to log-out of facebook in the browser session you're in, and also clear cache and/or cookies if that alone does not work, and try logging in to your WP site again. you then need to turn off the log-in through facebook in the plug-in settings or register your WP log-in account through facebook through his plug-in. that is what worked for me.
however, nowhere is this detail documented for his plug-in documented in the plug-in or plug-in page. this needs to be documented by otto, at least on the wordpress.org plug-in page. and also, the requested user bug reports, that it should not lock you out if you already have a valid log-in with your WP site simply because you haven't connected your log-in with facebook yet. that is a real issue here and needs to be addressed. it's just plain, simple, common UI/UX horse sense.
anyway, that's my input here on the workaround and the documentation and bug fix that is necessary here. we'll see if otto responds.