I changed my code as follows but the column still shows up as before (i.e., no change in the dropdown in column[5]) and no errors.
Thanks!
protected void NotamStatusDetails_InitializeLayout(object sender, Infragistics.WebUI.UltraWebGrid.LayoutEventArgs e)
{
e.Layout.Bands[0].FilterOptions.AllowRowFiltering = Infragistics.WebUI.UltraWebGrid.RowFiltering.OnServer;
e.Layout.Bands[0].Columns[1].AllowRowFiltering = false;
e.Layout.Bands[0].Columns[3].AllowRowFiltering = false;
e.Layout.Bands[0].Columns[4].AllowRowFiltering = false;
e.Layout.Bands[0].Columns[6].AllowRowFiltering = false;
e.Layout.Bands[0].Columns[5].FilterCollectionValues.Add("In Progress","<img src='Networks.Job.PastDue.png'/> In Progress");
e.Layout.Bands[0].Columns[5].FilterCollectionValues.Add("New","<img src='Networks.Job.PastDue.png'/> New");
e.Layout.Bands[0].Columns[5].FilterCollectionValues.Add("In Progress","<img src='Networks.Job.InProgress.png'/> In Progress");
e.Layout.Bands[0].Columns[5].FilterCollectionValues.Add("New","<img src='Networks.Job.InProgress.png'/> New");
e.Layout.Bands[0].Columns[5].FilterCollectionValues.Add("Completed","<img src='Networks.Job.Complete.png'/> Completed");
e.Layout.Bands[0].Columns[5].FilterCollectionValues.Add("Not Applicable","<img src='Networks.Job.Complete.png'/> Not Applicable");
}