Use RegEx in vba sub in general sheet

How to use regex in general vba sheet. i am getting lot of red lines and not able to find the reason for that.

I have enabled the Regularexpression vbScript also.

Private Const FCheckRgAddress As String = "A1:A100"
Private Sub Worksheet_Change(ByVal Target As Range)
'Update 20140905
    Dim a As String

    Set xChanged = Application.Intersect(Range(FCheckRgAddress), Target)
    If xChanged Is Nothing Then Exit Sub
End If

    Set xRegExp = CreateObject("VBScript.RegExp")
    xRegExp.Global = True
    xRegExp.IgnoreCase = True
    xRegExp.Pattern = "[^0-9a-z]"
    For Each xRg In xChanged
        If xRegExp.Test(xRg.Value) Then
            xHasErr = True
            Application.EnableEvents = False
            xRg.ClearContents
            Application.EnableEvents = True
        End If
    Next
    If a=1 Then

MsgBox "These cells had invalid entries and have been cleared:"
End If
End Sub


I got it from someother site, most of the lines are red

Plz help me