Regular Expression Not working for text box accepting only number.

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ASP.NET

I m using Regular expression in text box to accept only number but when i enter characters It is displaying the message "Enter only no " but when I click on update the character get saved in database.

I m using the following code

<asp:RegularExpressionValidator ID="RegularExpressionValidator2" runat="server"

                    ValidationExpression="(^[-]?[1-9]\d+$)|(^[-]?[1-9]$)|(^0$)|(^[-]?[1-9]\d+\.\d$)|(^[-]?[0-9]\.\d$)" ControlToValidate="txtcontactno"
                     ErrorMessage="Enter Number Only!" ForeColor="White"
                    ValidationGroup="check" Font-Size="Small" Display="Dynamic"></asp:RegularExpressionValidator>