I suggest you put a break during code execution, and manually select the control, and then try to figure the ID of the activeElement

Code:
    Dim ie As InternetExplorer    Dim obj As HTMLObjectElement
    Dim doc As HTMLDocument
    
    Set ie = New InternetExplorer
    ie.navigate "http://www.excelfox.com/forum/f2/unable-get-elementid-vba-ie-automation-851/"
    ie.Visible = True
    Do While ie.Busy: Loop
    Do While ie.readyState <> READYSTATE_COMPLETE: Loop
    Stop ' Now tab-activate the control, and come to this code again and push F8
    Set doc = ie.document
    MsgBox doc.activeElement.ID