I was trying to hide some summary rows in my grid, but once I hide a summary row, the program was become non-response.

There are code:
            UltraGridRow aRow = ultragrid1.GetRow(ChildRow.First);
            
            while (aRow!=null)
            {
                if (aRow.IsSummaryRow)
                {
                    aRow.Hidden = true;
                }
                aRow = aRow.GetSibling(SiblingRow.Next, true, true, true);

            }

I just want to hide some specific summary rows in the grid, how can I do that? Thank you very much!