Guys, Thank you so much, it works perfectly.
I was using :
=MID(CELL("filename",A1),FIND("]",CELL("filename",A1))+1,255) to get Tab Name to Cell A1 and then
Custom Data Validation =$A$1 <>"Master".
VBA: work great
Private Sub Worksheet_Change(ByVal Target As Range)
Application.EnableEvents = False
If Target.Cells.Count > 1 Then Exit Sub
If Not Intersect(Target, Range("C33:F52")) Is Nothing Then
Application.EnableEvents = False
cng = Target.Value
Application.Undo
Target.Value = Target.Value
Else
End If
Application.EnableEvents = True
End Sub