title: Update of multipicklist field not working in SalesForce?
body: <p>I wrote the following class in salesforce:</p>
  
  <pre><code>global class ChangeImmo implements Schedulable{
   // Execute method
      global void execute(SchedulableContext SC) {
          List&lt;Realty_User__c&gt; rs = [SELECT Buttons__c FROM Realty_User__c WHERE not (Buttons__c INCLUDES ('Terminplaner'))];
         for(Realty_User__c r : rs){
             r.Buttons__c += ';Terminplaner';
             update r;
         }                                                                           
      }
  }
  </code></pre>
  
  <p>Then I sheduled it for a one time run.</p>
  
  <p>It worked on our testbox, but not in the live version. We have 1700 users, of which around 730 don't have the "Terminplaner". Does someone know, why this is not working?</p>
  
  <p>Edit: I adjusted my code with the guide on DML exceptions by SalesForce and it is still not working:</p>
  
  <pre><code>global class ChangeImmo implements Schedulable {
  
      // Execute method
      global void execute(SchedulableContext SC) {
  
          for (List &lt; Realty_User__c &gt; lstRu: [SELECT Buttons__c FROM Realty_User__c WHERE not(Buttons__c INCLUDES('Terminplaner'))]) {
              for (Realty_User__c r : lstRu) {
                  r.Buttons__c += ';Terminplaner';
              }
              update lstRu;
          }
      }
  }
  </code></pre>
  
  <p>Edit 2: Okay I have found the debug log now and the error says:</p>
  
  <p>17:00:14.574 (10574150113)|FATAL_ERROR|System.ListException: Duplicate id in list: 003b000000ZAhDgAAL</p>