Try going into the console and seeing if the app is running anyway. Sometimes 500 errors spring up superfluously, even when things run fine. A small hiccup that we're working on aggressively.

Sinatra really isn't working.

We worked hard on Sinatra support this past weekend. Give it another shot. I've deployed multiple test Sinatra apps painlessly today, which was admittedly far less painless last week.

Same response with the Rackspace + Python setup. App is showed up in dashboard but I couldn't start it. Created domain returns a 404 page.