Control Iteration : Collection was modified; enumeration operation may not execute.

I'm trying to iterate through a pages controls, and while currently i've been successful setting controls to read only, i'd like to convert them to labels, to make for easy printing. Here is what i have, but when i run it, i get Collection was modified; enumeration operation may not execute.
I know that i'm adding/removing controls so that's why this is happening, but is there a better way to do this then taking the contents of the control, throwing it into a label, removing the original control and then adding the label control to the page?

Public Shared Sub SetFormToReadOnly(ByVal ctrl As System.Web.UI.Control)
            Dim txtTemp As TextBox
            Dim ddltemp As DropDownList
            Dim btnTemp As Button
            'iterate through each control in the page, and each controls' controls to get every
            'control on the masterpage/content page/ and and associated grouped controls, i.e. panels, etc.
            For Each subCtrl As Control In ctrl.Controls
                SetFormToReadOnly(subCtrl)
                If TypeOf subCtrl Is TextBox Then
                    txtTemp = subCtrl
                    txtTemp.ReadOnly = True
                    Dim tlabel As New Label
                    tlabel.Text = txtTemp.Text
                    ctrl.Controls.Remove(txtTemp)
                    ctrl.Controls.Add(tlabel)
                ElseIf TypeOf subCtrl Is DropDownList Then
                    ddltemp = subCtrl
                    ddltemp.Enabled = False
                   
                ElseIf TypeOf subCtrl Is Button Then
                    btnTemp = subCtrl
                    btnTemp.Enabled = False
                End If
            Next subCtrl
        End Sub