title: Unable to add foreign key constraint due to obscure conflict
body: <p>Trying to run :</p>
  
  <pre><code>ALTER TABLE [dbo].[Table1] ADD
  CONSTRAINT [FK_Table1_ScenarioResult] 
  FOREIGN KEY ([ScenarioResultID]) REFERENCES [dbo].[ScenarioResult] ([ScenarioResultID]) ON DELETE CASCADE
  </code></pre>
  
  <p>Getting this error :</p>
  
  <p><strong>Msg 547, Level 16, State 0, Line 1
  The ALTER TABLE statement conflicted with the FOREIGN KEY constraint "FK_Table1_ScenarioResult". The conflict occurred in database "8362", table "dbo.ScenarioResult", column 'ScenarioResultID'.</strong></p>
  
  <p>I have checked :</p>
  
  <ul>
  <li>Constraint does not already exist, and no other exists on same column</li>
  <li>The values in the column match in both tables</li>
  <li>Types of columns are the same</li>
  <li>Tried a different name, also fails</li>
  </ul>
  
  <p>On <code>SQL Server 2008 R2</code></p>
  
  <p>Any ideas what I could try?</p>