Failed to start DDE: value cannot be null

You may face a similar error message if you have incorrect values in the appsettings.json file:

Make sure you use escape characters correctly using the JSON format. For example the single backslash needs to be escaped as a double backslash.

A typical example is a connection string where this can happen, for example:

"Data Source=myserver\\VIRTDB,1433;Initial Catalog=virtdb;User Id=virtdb;Password=virtdb;"