regular+required validation

[loguin]

\[code\]<asp:TextBox ID="Textboxtotalamount" OnTextChanged="AmountChanged" Width="90px" AutoPostBack="true" runat="server"></asp:TextBox><asp:RequiredFieldValidator ID="RequiredFieldValidator" runat="server" ControlToValidate="Textboxtotalamount" SetFocusOnError="True" ValidationGroup="val">*</asp:RequiredFieldValidator><asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" ControlToValidate="Textboxtotalamount" ValidationExpression="^[-+]?[1-9]\d{0,13}(\.\d{1,3})?%?$" SetFocusOnError="True">F</asp:RegularExpressionValidator>\[/code\]in this above code can validate correctly.......but in text box i call "OnTextChanged"event ....suppose if i type(characters)in textbox errormesge shown at the same time ontextchanged event also called hen error occured ....i ve to stop OnTextChanged event when regularexpression raised......pls help