Here is a list of every test performed by Web Scan Service.
.NET Verbose Errors EnabledRemediation Task
Check server configuration
WASC ClassificationInformation Disclosure: Information LeakageAffected ProductsThis issue may affect different types of productsTechnical DescriptionAn ASP.NET application was deployed on the server with the switch on within the application’s web.config file.Fix Recommendation
Verify the web application and server configuration. The pure error text should not be displayed to the user.
Follow this msdn and you will find more hints about error handling:
http://msdn.microsoft.com/en-us/library/994a1482.aspx