Analysing the attached page, I found out the culprit of the issue is the VisibleStartTime property. I have reported this issue to the developer as a bug.

I will inform you if there is any update or progress regarding this issue.

I have reported this issue and the workaround to the developer. I will inform you if this fix will be included in the next hot patch. 

Edited 01/27/2010: The developer has agree to include the fix in the next hotfix

You will need to modify the window onload function to pass the WebGrid rowIndex to the display function. Here is the snippet:

var i;
var j;

var grid = ISGetObject("WGActivity");
var tblElm = grid.RootTable.GetElement(WG40.BODY, WG40.HTMLTABLE);

var no = tblElm.rows.length;
for (i = 0; i < tblElm.rows.length; i++) {
    for (j = 1; j < tblElm.rows[i].cells.length; j++) {
        var val = tblElm.rows[i].cells[j].innerText;
        if (tblElm.rows[i].cells[j].innerText != " ") {
            tblElm.rows[i].cells[j].innerHTML = "<INPUT id='h' TYPE=CHECKBOX  onClick='display(" + i + ");'>" + val;
        }
    }
}

return true;

The display function wil be responsible to add, modify, delete the item in the ListBox when user checked the CheckBox. Here is the snippet: 

function display(idx) {
    var grid = ISGetObject("WGActivity");
    var tblElm = grid.RootTable.GetElement(WG40.BODY, WG40.HTMLTABLE);
    
    var selRow = tblElm.rows[idx];    
    var optText = "";
    var optVal = "";
    
    for (j = 0; j < selRow.cells.length; j++) {
        var val = selRow.cells[j].innerText;
        if(j == 0)
            optVal = optText = val;
        if (val != " " && j > 0 && selRow.cells[j].getElementsByTagName("input")[0].checked)
            optText += " " + val;   
    }

    var listBox = document.getElementById("lbactivity");
    var doAdd = true;
    
    for (var i = 0; i < listBox.options.length; i++)
    {
        if (listBox.options[i].value == optVal) {
            doAdd = false;
            listBox.options[i].text = optText;
            if (optText == optVal)
                listBox.remove(i); 
            break;
        }
    }

    if (doAdd)
        document.getElementById("lbactivity").add(new Option(optText, optVal));
}

Have you used all the latest version of the dll? Our latest WebUI Framework is version 3 build 750 and ISDataSource version 1 build 211

If you already use all the latest version and build, please send us a sample project so we could analyse the issue further.

Based on my analysis of the snippet, I suspect that you are missing some field and table in the DataBinding propterty. Please compare it to one of the WebScheduler provided sample, such as Agenda_Navigation.aspx

The ISDS markup already contains a Category table, however you are not binding this table to the WebScheduler. The WebScheduler alsio already refrence the Categories table in the CategoriesDataMember.

In the RecurringEventsBinding property, some attribute is not assigned, such as EventIDField and ReminderDismiss.

I also see that the RecurrenceInfo table and RecurringEvents table contains a ScheduleID field in the ISDs which is not bound in the WebScheduler databinding.