title: Getting System.ComponentModel.INotifyDataErrorInfo error when accessing EF4 Entity from WCF Service
body: <p>I've got an EF4 class library, that is referenced in the web project of my Silverlight app.  The EF4 stuff works fine, and I can consume it properly in the Silverlight app.  I have an operation that is going to pull in 2 datasets of 60,000+ rows, compare them, and use one to update the other.  I've got that working in the Silverlight app, but i'm pretty sure it's the wrong place to do it, as there isn't any visual output, it is a data operation, so I created a Silverlight enabled WCF Service, and added the compare/update code into that, thinking it would be more correct to run it on the server, and just call it from the SL app.</p>
  
  <p>When I try and build the web project, I get the following error</p>
  
  <pre><code>The type 'System.ComponentModel.INotifyDataErrorInfo' is defined in an assembly that is not referenced.  You must add a reference to 'System.Windows, Version=2.0.5.0'
  </code></pre>
  
  <p>On this line of code</p>
  
  <pre><code>List&lt;x3Servers&gt; x3List = (from s in x3Context.x3Servers select s).ToList();
  </code></pre>
  
  <p>Where x3Servers is an entity in my data library, and x3Context is set to the data model, services entities object (XSDataLibrary.Models.xSightEntities).</p>
  
  <p>I believe this is to do with INotifyDataErrorInfo being moved from System, to System.Windows for Silverlight apps.  I can't include System.Windows as it is a web project, but am assuming it's possible to use EF4 entities in a Silverlight enabled WCF service (or perhaps that's where i'm going wrong).</p>
  
  <p>Any help or advice on how to consume EF4 stuff from a WCF service (which can be called from a Silverlight app), or how tto avoid this error would be most appreciated.</p>
  
  <p>Thanks</p>
  
  <p>Mick</p>