title: Error Account with Id = "xxxxxx" does not exist
body: <p>I have a custo workflow that creates an account and opportunities.</p>
  
  <p>Sometimes I have this error: Account with Id = "xxxxxx" does not exist.</p>
  
  <p>I don't know what's wrong in my code knowing that I find the account in the CRM.<br>
  Here are the steps of my plugin code:</p>
  
  <ol>
  <li>Find the account by num (if it doesn't exist, I create them)</li>
  <li>Get the account = Account</li>
  <li>Create an opportunity with Opportunity["parentaccountid"] = Account;</li>
  <li>Error message !</li>
  </ol>
  
  <p>Code:</p>
  
  <pre class="lang-cs prettyprint-override"><code>//Get opportunity
  Guid id = retrieveOpportunity&lt;string&gt;("opportunity", "new_numero", numero, service);
  Entity eOpportunity;
  if (id != Guid.Empty)
  {
      eOpportunity = new Entity("opportunity", id);
  }
  else
  {
      eOpportunity = new Entity("opportunity");
  }
  
  //Get account
  EntityReference eAccount = retrieveAccount&lt;string&gt;(accountCode, "account", "new_code", service);
  if (eAccount == null)
  {
      eAccount = new Entity("account", "new_code", accountCode);
      eAccount["name"] = "name";
      UpsertRequest usMessage = new UpsertRequest()
      {
          Target = eAccount
      };
      //create account
      UpsertResponse usResponse = (UpsertResponse)this._service.Execute(usMessage);
      eOpportunity["parentaccountid"] = usResponse.Target;
  }
  else
  {
      eOpportunity["parentaccountid"] = eAccount;
  }
  
  UpsertRequest req = new UpsertRequest()
  {
      Target = eOpportunity
  }; 
  //upsert opportunity
  UpsertResponse resp = (UpsertResponse)service.Execute(req);
  
  if (resp.RecordCreated)
      tracer.Trace("New opportunity");
  else
      tracer.Trace("Opportunity updated");
  </code></pre>
  
  <p>Sometimes there are several workflows that are started at the same time and that do the same thing (creating other opportunities)</p>