in Web.config how to solve Configuration Error

You can clean your solution and rebuild it. Then restart your Visual studio and build it again. See if it release mode or debug mode - make it debug mode.

 

Secondly you have not referred the local path when you opened the application in visual studio. 

 

Go through below article and follow it:

 

http://www.aspsnippets.com/Articles/Issue---allowDefinition-MachineToApplication-beyond-application-level.aspx