I can't remember the exact point of change, but remember that Dispatcher changed into ActionController::Dispatcher somewhere along the line - obviously after Rails 1.2.3 and 1.2.6!

There was already a check in place within Thin to see if the call method could be used on the Dispatcher - the trouble being that because ActionController::Dispatcher isn't defined then it fails!

I've submitted a ticket - a simple check to make sure ActionController::Dispatcher is defined - in the meantime then i've also put a patch up as a gist to get things running.