This is a quick post. I was getting HTTP 500 errors when deploying my new site to AppHarbor. Long story short, if you've brought down the DotNetAuth Nuget package, it adds this to your
<section name="uri" type="System.Configuration.UriSection, System, Version=126.96.36.199, Culture=neutral, PublicKeyToken=b77a5c561934e089" />
AppHarbor already has this defined and it is throwing a duplicate web.config section exception. Remove this line and you should be A-OK!