title: ASP.NET Web Api Error The 'ObjectContent`1' type failed to serialize the response body for content type 'application/xml; charset=utf-8'
body: <p>I have created 2 tables. Test table with ( ID, name, group_id ) fields and group_master with ( group_id, group_name ).</p>
  
  <p>The group_id from Test table relationship with the group_master group_id.</p>
  
  <p>If i have not set a relationship key, the web api is working fine and returning me the list as xml.</p>
  
  <p>If there is an reference to another table, the web api is throwing an error.</p>
  
  <p><strong>"The 'ObjectContent`1' type failed to serialize the response body for content type 'application/xml; charset=utf-8'"</strong></p>
  
  <p>This happens only fields with relationship.</p>
  
  <p>What could be the issue and important this "<strong>I am new to .net</strong>".</p>
  
  <p>Thanks!</p>