When you created a reporting program that worked fine until added a chart to it. And you would get the error below
"Could not load file or assembly 'System.Windows.Forms.DataVisualization, Version=126.96.36.199, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified"
Reason: That means you should have MS chart installed in the web server.
As .Net 4.0 has MS chats built in, you just need to login to your hosting account-->hosting manager
-->website domain manager to change the site type to asp.net 4.0 to solve it.