[VB6] - using a string control name for catch it's properties

[joaquim]

i use these code for catch the Top and Left of a control string Name(in a property):

lngOldScrollObjectY = UserControl.Parent.Controls(strObjectScroll).Top
        lngOldScrollObjectX = UserControl.Parent.Controls(strObjectScroll).Left

what is strange is that i get an error message:
"728 - is not legal control name"
and these property activate 1 timer. and in a timer i have these that don't gives me an error:

If UserControl.Parent.Controls(strObjectScroll).Top > lngOldScrollObjectY Then
        ScrollingVertical.Value = ScrollingVertical.Value + UserControl.Parent.Controls(strObjectScroll).Top + lngOldScrollObjectY
        lngOldScrollObjectY = UserControl.Parent.Controls(strObjectScroll).Top
        
    ElseIf UserControl.Parent.Controls(strObjectScroll).Top < lngOldScrollObjectY Then
        ScrollingVertical.Value = ScrollingVertical.Value - UserControl.Parent.Controls(strObjectScroll).Top - lngOldScrollObjectY
        lngOldScrollObjectY = UserControl.Parent.Controls(strObjectScroll).Top
        
    ElseIf UserControl.Parent.Controls(strObjectScroll).Left > lngOldScrollObjectX Then
        ScrollingVertical.Value = UserControl.Parent.Controls(strObjectScroll).Left - lngOldScrollObjectX
        lngOldScrollObjectX = UserControl.Parent.Controls(strObjectScroll).Left
        
    ElseIf UserControl.Parent.Controls(strObjectScroll).Left < lngOldScrollObjectX Then
        ScrollingVertical.Value = UserControl.Parent.Controls(strObjectScroll).Left + lngOldScrollObjectX
        lngOldScrollObjectX = UserControl.Parent.Controls(strObjectScroll).Left        
    End If

that's strange. how can i avoid that error?
(these usercontrol is a container and these string control name is a control name that is inside of usercontrol)