In vb6.0, one child window, e.g. frmSub1 here, can call the function or execute the procedure in another child window, e.g. frmSub2 here, like my following MDI program:

'frmMDI
Private Sub mNewSub1_Click()
    Dim frm As New frmSub1
    frm.Show
End Sub

Private Sub mNewSub2_Click()
    Dim frm As New frmSub2
    frm.Show
End Sub

'frmSub1
'Get the sum by call the frmSub2's Function
Private Sub Command1_Click()
    Dim f As Form
    For Each f In Forms
        If TypeOf f Is frmSub2 Then
            Text1.Text = f.fSum(Val(Text1.Text)) ¡®can call fSum function in frmSub2 correctly.
        End If
    Next f
End Sub

'Do the frmSub2's procedure and give the sum
Private Sub Command2_Click()
    Dim f As Form
    For Each f In Forms
        If TypeOf f Is frmSub2 Then
            Call f.pSum(Val(Text1.Text)) ¡®Can execute pSum procedure in frmSub2 correctly.
        End If
    Next f
End Sub

'frmSub2
Public Function fSum(j As Integer) As Integer
    Dim i As Integer, sum As Integer
    For i = 1 To j
        sum = sum + i
    Next i
    fSum = sum
End Function

Public Sub pSum(j As Integer)
    Dim i As Integer, sum As Integer
    For i = 1 To j
        sum = sum + i
    Next i
    Text1.Text = sum
End Sub

'Get the sum by Function
Private Sub Command1_Click()
    Text1.Text = fSum(Val(Text1.Text))
End Sub

'Get the sum by Procedure
Private Sub Command2_Click()
    Call pSum(Val(Text1.Text))
End Sub

This MDI program can be done in VB6.0 very well. But when I upgrade it into vb2005, it counts the following errors in frmSub1:
Error 1: ¡°fSum¡± is not the ¡°System.Windows.Forms.Form" member.
Error 2: ¡°pSum¡± is not the ¡°System.Windows.Forms.Form" member.

Please help me solve the problem. Thank you very much.
LingYong He, from China

Thanks for dear Billy, he told me how to get around my problem as following:

Origianl code:
    Dim f As Form
    For Each f In Forms
        If TypeOf f Is frmSub2 Then
            Text1.Text = f.fSum(Val(Text1.Text))
        End If
    Next f
Modified code:
    Dim f As Form
    For Each f In Forms
        If TypeOf f Is frmSub2 Then
            Dim f2 As frmSub2 ' Added
            f2=CType(f, frmSub2) ' Added
            Text1.Text = f2.fSum(Val(Text1.Text)) ' Modified
        End If
    Next f
Thanks all of you who paid attention to my question as well.