R – website compile error

I am experiencing the following error while loading a website:

Server Error in '/DatingGridView' Application.
Configuration Error
Description: An error occurred during the processing of a configuration file required to service this request. Please review the specific error details below and modify your configuration file appropriately.

Parser Error Message: Could not load file or assembly 'System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.

Source Error:

Line 52:        
Line 53:            
Line 54:                
Line 55:            
Line 56:        


Source File: D:\VSProjects\DatingGridView\web.config    Line: 54

Assembly Load Trace: The following information can be helpful to determine why the assembly 'System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' could not be loaded.

=== Pre-bind state information ===
LOG: User = PassionFruit-PC\PassionFruit!!!
LOG: DisplayName = System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
 (Fully-specified)
LOG: Appbase = file:///D:/VSProjects/DatingGridView/
LOG: Initial PrivatePath = D:\VSProjects\DatingGridView\bin
Calling assembly : (Unknown).
===
LOG: This bind starts in default load context.
LOG: Using application configuration file: D:\VSProjects\DatingGridView\web.config
LOG: Using machine configuration file from C:\Windows\Microsoft.NET\Framework\v2.0.50727\config\machine.config.
LOG: Post-policy reference: System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
LOG: Attempting download of new URL file:///C:/Users/PassionFruit!!!/AppData/Local/Temp/Temporary ASP.NET Files/datinggridview/5a514f00/39d65547/System.Web.Extensions.DLL.
LOG: Attempting download of new URL file:///C:/Users/PassionFruit!!!/AppData/Local/Temp/Temporary ASP.NET Files/datinggridview/5a514f00/39d65547/System.Web.Extensions/System.Web.Extensions.DLL.
LOG: Attempting download of new URL file:///D:/VSProjects/DatingGridView/bin/System.Web.Extensions.DLL.
LOG: Attempting download of new URL file:///D:/VSProjects/DatingGridView/bin/System.Web.Extensions/System.Web.Extensions.DLL.
LOG: Attempting download of new URL file:///C:/Users/PassionFruit!!!/AppData/Local/Temp/Temporary ASP.NET Files/datinggridview/5a514f00/39d65547/System.Web.Extensions.EXE.
LOG: Attempting download of new URL file:///C:/Users/PassionFruit!!!/AppData/Local/Temp/Temporary ASP.NET Files/datinggridview/5a514f00/39d65547/System.Web.Extensions/System.Web.Extensions.EXE.
LOG: Attempting download of new URL file:///D:/VSProjects/DatingGridView/bin/System.Web.Extensions.EXE.
LOG: Attempting download of new URL file:///D:/VSProjects/DatingGridView/bin/System.Web.Extensions/System.Web.Extensions.EXE.


Version Information: Microsoft .NET Framework Version:2.0.50727.1433; ASP.NET Version:2.0.50727.1433