You must add a reference to assembly 'System.Runtime, Version=4.0.0.0, Culture=neutral, Pu code example
Example: you must add a reference to assembly 'System.Core, Version=4.0.0.0, Culture=neutral
//place this in the web.config file
<add assembly="System.Core, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
<add assembly="System.Data.DataSetExtensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
<add assembly="System.Xml.Linq, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>