Mega Code Archive
Use Intersect when you want to find the cells that are common to two or more ranges, or in other words, where the ranges overlap
Private Sub Worksheet_SelectionChange(ByVal Target As Range)
Dim rngForbidden As Range
Set rngForbidden = Union(Range("B10:F20"), Range("H10:L20"))
'If selection does not overlap forbidden areas, do nothing
If Intersect(Target, rngForbidden) Is Nothing Then Exit Sub
Range("A1").Select
MsgBox "You can't select cells in " & rngForbidden.Address, vbCritical
End Sub