Virtual directory in IIS

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C#

ASP.NET

IIS8

In my project i need to add a virtual directory in iis root folder.In root folder there is a .net 4 framwork application and the new application(web api) create in 4.5.2 framwork.
i need to add the web api application in iis website as a virtual directory.
i add this. after add i call via url. there is a error. in this error the application need root application dll dependencies.
The error is

Could not load file or assembly 'Checkbox.Web' or one of its dependencies. The system cannot find the file specified.

how to solve the problem. Thank you

What I have tried:

add the application in virtual directory and then the directory convert to application.