Getting an error after migrating VS2012 to VS2013 .

Hi,

I have installed VS2013 and opened my project.

So web.config added "  <add assembly="System.Spatial, Version=5.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />"

and giving compile error :

"Could not load file or assembly 'System.Spatial, Version=5.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.D:\My Work\EFMS\Main\web.config16"

Please help me to solve this.. 

Thank  you.