Visual Basic - Not allowing cell entry

Its not working, when I insert it into the field, it tells me "Ambugious name detected:Worksheet_Change"

Your part is towards the end....
This is how it looks:

Private Sub Worksheet_Activate()

End Sub

Private Sub Worksheet_Change(ByVal Target As Excel.Range)
'this is all for validation of user input on the details sheet

'make sure a date has been input in E11 and E12
If Target.Cells(1, 1).Address(0, 0) = "E11" Then
    If Target.Cells(1, 1) <> "" And Not IsDate(Target.Cells(1, 1)) Then
        MsgBox "You must input a date!", vbExclamation, "DATE REQUIRED"
        Target.Cells(1, 1) = ""
        Exit Sub
    End If
End If
If Target.Cells(1, 1).Address(0, 0) = "E12" Then
    If Target.Cells(1, 1) <> "" And Not IsDate(Target.Cells(1, 1)) Then
        MsgBox "You must input a valid date!", vbExclamation, "DATE REQUIRED"
        Target.Cells(1, 1) = ""
        Exit Sub
    End If
End If

'make sure enddate>=startdate
If Sheets("Salary Detail").Range("enddate") <> "" And Sheets("Salary Detail").Range("startdate") <> "" Then
    If Sheets("Salary Detail").Range("enddate") < Sheets("Salary Detail").Range("startdate") Then
        MsgBox "We've heard of short projects before, but this one really takes the cake!", vbExclamation, "END DATE BEFORE START DATE"
        Sheets("Salary Detail").Range("enddate") = ""
        Exit Sub
    End If
End If
    
'make sure enddate<=startdate + 366
If Sheets("Salary Detail").Range("enddate") <> "" And Sheets("Salary Detail").Range("startdate") <> "" Then
    If Sheets("Salary Detail").Range("enddate") > Sheets("Salary Detail").Range("startdate") + 366 Then
        MsgBox "This project has a very long initial year!", vbExclamation, "END DATE BEFORE START DATE"
        Sheets("Salary Detail").Range("enddate") = ""
        Exit Sub
    End If
End If

'make sure FTE's in C23:C62  and the levels of effort in H23:H62 are in the range 0-1
If Target.Column = 3 Or Target.Column = 8 Then
    If Target.Row >= 23 And Target.Row <= 62 Then
        If Not IsNumeric(Target.Cells(1, 1)) Then
            MsgBox "You must enter a number between 0 and 1!", vbExclamation, "NUMBER BETWEEN 0 AND 1 REQUIRED"
            Target.Cells(1, 1) = ""
            Exit Sub
        ElseIf Target.Cells(1, 1) < 0 Or Target.Cells(1, 1) > 1 Then
            MsgBox "You must enter a number between 0 and 1!", vbExclamation, "NUMBER BETWEEN 0 AND 1 REQUIRED"
            Target.Cells(1, 1) = ""
            Exit Sub
        End If
    End If
End If

'make sure the salaries in E23:E62 are positive numbers
If Target.Column = 5 Then
    If Target.Row >= 23 And Target.Row <= 62 Then
        If Not IsNumeric(Target.Cells(1, 1)) Then
            MsgBox "You must enter a number!", vbExclamation, "NUMBER GREATER THAN 0 REQUIRED"
            Target.Cells(1, 1) = ""
            Exit Sub
        ElseIf Target.Cells(1, 1) < 0 Then
            MsgBox "You're getting paid that badly!?", vbExclamation, "NUMBER GREATER THAN 0 REQUIRED"
            Target.Cells(1, 1) = ""
            Exit Sub
        End If
    End If
End If

'make sure the fringe benefit types in P23:P62 are appropriate
If Target.Column = 16 Then
    If Target.Row >= 23 And Target.Row <= 62 Then
        If Target.Cells(1, 1) <> "" And Target.Cells(1, 1) <> "F" And Target.Cells(1, 1) <> "U" And Target.Cells(1, 1) <> "A" And Target.Cells(1, 1) <> "P" And Target.Cells(1, 1) <> "T" And Target.Cells(1, 1) <> "R" And Target.Cells(1, 1) <> "S" And Target.Cells(1, 1) <> "W" And Target.Cells(1, 1) <> "f" And Target.Cells(1, 1) <> "a" And Target.Cells(1, 1) <> "p" And Target.Cells(1, 1) <> "t" And Target.Cells(1, 1) <> "r" And Target.Cells(1, 1) <> "u" And Target.Cells(1, 1) <> "s" And Target.Cells(1, 1) <> "w" Then
            MsgBox "You must enter a fringe benefit code from the list above!", vbExclamation, "'F','A','P','T','R','S', OR 'W' REQUIRED"
            Target.Cells(1, 1) = ""
            Exit Sub
        End If
    End If
End If
 
    
    If Target.Row >= 23 And Target.Row <= 62 Then
'make sure the project duration in L10 is a positive number
If Target.Column = 12 And Target.Row = 10 Then
        If Not IsNumeric(Target.Cells(1, 1)) Then
            MsgBox "You must enter a number!", vbExclamation, "NUMBER GREATER THAN 0 REQUIRED"
            Target.Cells(1, 1) = ""
            Exit Sub
        ElseIf Target.Cells(1, 1) < 0 Then
            MsgBox "Are you sure the project is that short?", vbExclamation, "NUMBER GREATER THAN 0 REQUIRED"
            Target.Cells(1, 1) = ""
            Exit Sub
        End If
End If
End If

Private Sub Worksheet_Change(ByVal Target As Range)
    Dim r       As Range
    Dim cell    As Range

    Set r = Intersect(Target, Rows("23:62"), Union(Columns("P"), Columns("R")))
    If r Is Nothing Then Exit Sub

    For Each cell In r
        With cell
            If .Column = Columns("P").Column Then
                If .Value = "U" And Not IsEmpty(Cells(.Row, "R").Value) Then
                    With Cells(.Row, "R")
                        .ClearContents
                        .Select
                        MsgBox "Must be blank.", vbOKOnly
                    End With
                End If

            Else    ' it's in column R
                If Cells(.Row, "P").Value = "U" And Not IsEmpty(.Value) Then
                    .ClearContents
                    .Select
                    MsgBox "Must be blank.", vbOKOnly
                End If
            End If
        End With
    Next cell
End Sub