Error 1 The type or namespace name 'Linq' does not exist in the namespace 'System' (are you missing an assembly reference?)
Solution:
Make sure to include the reference to system.core dll ( version 3.5.0.0)
<system.web>
<compilation debug="false">
<assemblies>
<add assembly="System.Core, Version=3.5.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
</assemblies>
</compilation>
</system.web>