try this one ,.. without regular expressions to restrict input text...
<asp:TextBox ID="txtSearch" runat="server" ></asp:TextBox>
<ajaxToolkit:FilteredTextBoxExtender ID="fteSearch" runat="server" TargetControlID="txtSearch" FilterMode="InvalidChars"
InvalidChars=";|~!@#$%^*<>/\{}:';/*+_~`[]="">
</ajaxToolkit:FilteredTextBoxExtender>