here is my code, I receive an error message "variable not defined"

Option Explicit
Dim Element As Integer

'~~~ Creating the type
Private Type Student
strName As String
intMark As Integer
End Type
Private Sub cmdAddRecord_Click()

'~~~ Checking. This should be done first !
If Val(txtStudentMark.Text) <= 0 Then
MsgBox "student mark cannot be less than zero. Please re-enter it"
Exit Sub
ElseIf Val(txtStudentMark.Text) > 100 Then
MsgBox "student mark cannot be greater than 100. Please re-enter it"
Exit Sub
End If

Element = Element + 1
ReDim Preserve strName(1 To Element) <---------------error msg "variable not defined"
ReDim Preserve intMark(1 To Element)

strName(Student) = txtStudentName.Text
intMark(Student) = txtStudentMark.Text

lstNames.AddItem Student(Element).strName
lstMarks.AddItem Student(Element).intMark

End Sub

I thought it was though above? Have I declared the datatypes correctly?