[DevExpress Support Team: CLONED FROM T648219: Dashboard create data source error - ConnectionStrings provider is not configured]
You guys need to update your Tutorial on creating a new dashboard project.
https://www.youtube.com/watch?v=K4zaPGQ-YkU
This is a link from this page:https://www.devexpress.com/Support/Demos/#dashboard How to Create a Web Designer and Viewer (ASP.NET MVC)
We shouldn't have to go and search the web and try to find a way to fix it when following your tutorial. While you are at it, you could update the tutorial as your current template is different and more options are there.
For anyone else who has found this page when encountering this problem, add this code to the application_start
DevExpress.DashboardWeb.DashboardConfigurator.Default.SetConnectionStringsProvider(new DevExpress.DataAccess.Web.ConfigFileConnectionStringsProvider());