I try this:
_explorerBar.ActiveItem = _explorerBar.Groups[0].Items[0];

but get this Exception:
"ActiveItem cannot be set - specified Item cannot be activated! (Item may be disabled or have a style that is not activatable like Separator or Label)"

_explorerBar.Groups[0].Items[0] is this:
UltraExplorerBarItem item = new UltraExplorerBarItem(sectionId.ToString());
item.Text = sectionText;
_explorerBar.Groups[0].Items.Add(item);

What am I missing?