title: Update Task Project using CSOM
body: <p>I'm trying to update a task in microsoft project online using CSOM but it's not working always return me a exception ("Unknown Error").
  I'm using a example this example: 
  <a href="https://github.com/OfficeDev/Project-CSOM-My-Task-Checklist" rel="nofollow noreferrer">https://github.com/OfficeDev/Project-CSOM-My-Task-Checklist</a></p>
  
  <p>Assignment assignment;</p>
  
  <pre><code>            // Loop through each assignment and update % complete
              for (int j = 0; j &lt; chkAssignments.Items.Count; j++)
              {
                  assignment = (Assignment)chkAssignments.Items[j];
  
                  if (assignment.Dirty)
                  {
                      if (assignment.Done)
                      {
                          self.Assignments[j].PercentComplete = 100;
                          self.Assignments[j].Comments = "teste Osmar";
                      }
                      else
                      {
                          self.Assignments[j].PercentComplete = 0;
                      }
                  }
              }
  
  
              // Update the assignments and submit the status updates.
              self.Assignments.Update();
  
              self.Assignments.SubmitAllStatusUpdates("");
              projContext.ExecuteQuery();
  </code></pre>