title: StrongTypingException in Linq
body: <p>Anybody can tell why the ToList() throws an exception?</p>
  
  <pre><code>var duplicates =  
      from typeMappings in _liveTable.Where(r =&gt;
          (r.ProviderId == providerId) &amp;&amp; (r.ExchangeId == exchangeId))
      join dataDictionary in _liveDataSet.DataDictionary.Where(r =&gt; 
          (r.DataDictionaryTypeId == dataDictionaryTypeId)) 
      on typeMappings.DataDictionaryId equals dataDictionary.DataDictionaryId
      select typeMappings.ConfigId;
  
  if (duplicates.ToList().Count &gt; 0) 
  { ... }
  </code></pre>
  
  <p>The Exception message is:<br>
      'duplicates.ToList()' threw an exception of type 'System.Data.StrongTypingException' System.Collections.Generic.List {System.Data.StrongTypingException}</p>
  
  <p>Thanks</p>