Hallo Detlev,

grade erst deinen neuen Beitrag gesehen, eine Prozedur dafür zu verwenden ist natürlich besser als meine Lösung, welche auch garnicht so funktioniert, wie ich grade festgestellt habe. Bin bei dir allerdings auch skeptisch, woher nimmst du die Variable "tb1"?

Ich würd's so machen:

'check if value is numeric and stop if it isnt
Private Sub Check(str$, Key As MSForms.ReturnInteger)
    If Not IsNumeric(str & Chr(Key)) Then
        Key = 0
        Beep
    End If
End Sub

Private Sub TextBox2_KeyPress(ByVal KeyAscii As MSForms.ReturnInteger)
    Check ActiveControl.Text, KeyAscii
End Sub

Insgesamt dann so:

Option Explicit

Dim Bereich As Range
Dim Zellen() As Range

Private Sub UserForm_Initialize()
    ZellenEinlesen
End Sub
Private Sub UserForm_Activate()
    'Erstes Auswahlfeld Markieren
    With TextBox2
        .SetFocus
        .SelStart = 0
        .SelLength = Len(.Text)
    End With
     
    'Überschrift
    Me.TextBox1.Value = ActiveSheet.Range("B36").Text
    
    Dim i%
    For i = 0 To 11
       Me.Controls("TextBox" & i + 2).Text = Zellen(i).Value
    Next
     
End Sub
Private Sub ZellenEinlesen()
    Dim E1%, E2%

    Set Bereich = Range("E28:G31")
    With Bereich
        E1 = .Rows.Count
        E2 = .Columns.Count
    End With
    
    ReDim Zellen(E1 * E2 - 1)
    Dim r%, c%, i%
    For r = 1 To E1
        For c = 1 To E2
            Set Zellen(i) = Bereich(r, c)
            i = i + 1
        Next
    Next

End Sub

Private Sub CommandButton1_Click()
    
    Dim i%
    For i = 2 To 13
        If Me.Controls("TextBox" & i).Text = "" Then
            MsgBox ("Bitte einen Wert eingeben")
            Exit For
        End If
    Next
    If i > 13 Then Exit Sub
    
    For i = 0 To 11
        Zellen(i).Value = Me.Controls("TextBox" & i + 2).Text
    Next
        
    UF_Tabelle_01.Hide 'hier eintragen
End Sub
Private Sub CommandButton1_MouseMove(ByVal Button As Integer, ByVal Shift As Integer, ByVal x As Single, ByVal Y As Single)
    CommandButton1.SetFocus
End Sub
Private Sub CommandButton2_Click()
    UF_Tabelle_01.Hide 'hier eintragen
End Sub
Private Sub CommandButton2_MouseMove(ByVal Button As Integer, ByVal Shift As Integer, ByVal x As Single, ByVal Y As Single)
    CommandButton2.SetFocus
End Sub
Private Sub CommandButton3_Click()
    
    Dim x As Range
    For Each x In Zellen
        x = 0
    Next
    
    Unload Me
    UF_Tabelle_01.Show 'hier eintragen
End Sub
Private Sub CommandButton3_MouseMove(ByVal Button As Integer, ByVal Shift As Integer, ByVal x As Single, ByVal Y As Single)
    CommandButton3.SetFocus
End Sub

'check if value is numeric and stop if it isnt
Private Sub Check(str$, Key As MSForms.ReturnInteger)
    If Not IsNumeric(str & Chr(Key)) Then
        Key = 0
        Beep
    End If
End Sub

Private Sub TextBox2_KeyPress(ByVal KeyAscii As MSForms.ReturnInteger)
    Check ActiveControl.Text, KeyAscii
End Sub
Private Sub TextBox3_KeyPress(ByVal KeyAscii As MSForms.ReturnInteger)
    Check ActiveControl.Text, KeyAscii
End Sub
Private Sub TextBox4_KeyPress(ByVal KeyAscii As MSForms.ReturnInteger)
    Check ActiveControl.Text, KeyAscii
End Sub
Private Sub TextBox5_KeyPress(ByVal KeyAscii As MSForms.ReturnInteger)
    Check ActiveControl.Text, KeyAscii
End Sub
Private Sub TextBox6_KeyPress(ByVal KeyAscii As MSForms.ReturnInteger)
    Check ActiveControl.Text, KeyAscii
End Sub
Private Sub TextBox7_KeyPress(ByVal KeyAscii As MSForms.ReturnInteger)
    Check ActiveControl.Text, KeyAscii
End Sub
Private Sub TextBox8_KeyPress(ByVal KeyAscii As MSForms.ReturnInteger)
    Check ActiveControl.Text, KeyAscii
End Sub
Private Sub TextBox9_KeyPress(ByVal KeyAscii As MSForms.ReturnInteger)
    Check ActiveControl.Text, KeyAscii
End Sub
Private Sub TextBox10_KeyPress(ByVal KeyAscii As MSForms.ReturnInteger)
    Check ActiveControl.Text, KeyAscii
End Sub
Private Sub TextBox11_KeyPress(ByVal KeyAscii As MSForms.ReturnInteger)
    Check ActiveControl.Text, KeyAscii
End Sub
Private Sub TextBox12_KeyPress(ByVal KeyAscii As MSForms.ReturnInteger)
    Check ActiveControl.Text, KeyAscii
End Sub
Private Sub TextBox13_KeyPress(ByVal KeyAscii As MSForms.ReturnInteger)
    Check ActiveControl.Text, KeyAscii
End Sub