'Is the character illegal? If so replace it in workingName
If IsError(Application.Match(Mid(inputName, i, 1), validchars, 0)) Then

'Detect whether the first character in workingName is a number.
Dim numbers() As Variant
numbers = Array("1", "2", "3", "4", "5", "6", "7", "8", "9", "0")

If Not IsError(Application.Match(Mid(workingName, 1, 1), numbers, 0)) Then

If Not IsNumeric(Left(workingName,1)) Then

Public Function ContainsAny(ByVal string_source As String, ByVal caseSensitive As Boolean, ParamArray find_strings() As Variant) As Boolean

    Dim find As String, i As Integer, found As Boolean

    For i = LBound(find_strings) To UBound(find_strings)

        find = CStr(find_strings(i))
        found = Contains(string_source, find, caseSensitive)

        If found Then Exit For
    Next

    ContainsAny = found

End Function

If Not ContainsAny(Mid(inputName,i,1), False, "_", _
    "1", "2", "3", "4", "5", "6", "7", "8", "9", "0", _
    "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", _
    "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z") _
Then
    'character is illegal
End If