Hi,
The message box appearing, because, once you clear the textbox, again its a textchange event, so, it is becoming an infinite function.
so, try below code.
If TextBox1.Text.Trim <> "" Then
If Not IsNumeric(TextBox1.Text) Then
Dim abc As DialogResult = MessageBox.Show("Please insert numeric only!", "Error!!", MessageBoxButtons.OKCancel)
If abc = DialogResult.OK Then
TextBox1.Clear()
End If
End If
End If
hope it helps