[Resolved] Error CS0012: The type 'System.Object' is defined in an assembly that is not referenced. You must add a reference to assembly

How to fix error CS0012: The type 'System.Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Runtime, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' 

How to Fix:

Check in the web.config and Replace from:

<compilation targetFramework="4.5" />

 Replace to:

<compilation debug="true" targetFramework="4.5">
<assemblies>
<add assembly="System.Runtime, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />
</assemblies>
</compilation>

Hope it can help.