Could not load file or assembly 'Facebook.Web'

I'm a newbie in C# and I encounters this error when I plot in the app ID, secret and URLs. What did I do wrong/miss out?

Parser Error Message: Could not load file or assembly 'Facebook.Web' or one of its dependencies. The system cannot find the file specified.

Source Error:

Line 22:       <httpHandlers>
Line 23:         <add verb="*" path="facebookredirect.axd" 
Line 24:                       type="Facebook.Web.FacebookAppRedirectHttpHandler, Facebook.Web" />
Line 25:       </httpHandlers>
Line 开发者_运维百科26:    </system.web>

Do you have Facebook.Web.dll in the bin directory of your web application?