<eo:ProgressBar ID="ProgressBar1" runat="server"
            BorderColor="Black" BorderStyle="Solid"
            BorderWidth="1px" ControlSkinID="None"
            Height="13px"
            IndicatorColor="Red"
            ShowPercentage="True" Value="0"
            DesignOptions-BackColor="Red"
            ClientSideOnValueChanged="OnProgress"
            ClientSideOnTaskDone="Done"
            OnRunTask="ProgressBar1_RunTask">
        </eo:ProgressBar>"

if (!e.IsStopped)   //if the progress bar still hasn't been stopped
{
      e.UpdateProgress(progressMade, msg);   //doesn't actually seem to do anything
      e.UpdateProgress(progressMade, msg);   //will actually make it to the client side web page and update appropriately

//trying with only one call to UpdateProgress each time instead of twice in a row, just to see what happens
e.UpdateProgress(0, "Running...<br>");         //when this does work, which is rare, but I have seen it work...

//...
//code here
//...

//next update
e.UpdateProgress(progressMade, msg);       //...this one doesnt

for (int i = 0; i < requiredNoteIDs.Count; i++)
{
      if (!e.IsStopped)      //check this just in case between the last iteration and this one
                                  //the Stop button has been pressed, making e unavailable
      {
           //main stuff is done here

           didEOUpdate = e.UpdateProgress(progressMade, msg);
           currentIterations++;

           //if the progress bar did NOT update
           if (!didEOUpdate)
                break;

           System.Threading.Thread.Sleep(1000);
      }
      else
      {
           break;
      }
}//for loop

<button id="btnStopTest" class="button floatRight" tabindex="22" disabled="disabled" onclick="Stop();">Stop Test</button>

function Stop() {
    unsetHourglass();

    // Stop progress bar
    eo_GetObject("ProgressBar1").stopTask();

    var txtBox = document.getElementById(OutputLabelClientID);
    txtBox.innerHTML = txtBox.innerHTML + "Testing was stopped.";
}