SCRIPT5009: 'DefaultButtonKeyPress' is undefined issue in IE

Hi

I am getting follwoing script in IE only " SCRIPT5009: 'DefaultButtonKeyPress' is undefined " when pressing any key
My code is like
<asp:Literal ID="lblUserName" runat="server"
Text="UserName" /></label>
<asp:TextBox ID="txtUserName" runat="server" />
<asp:RequiredFieldValidator ID="rfvEmail" runat="server" ControlToValidate="txtUserName"
ErrorMessage="UserName Required" Display="Dynamic" Text="*" SetFocusOnError="True" />


When it run in IE it get converted into
<label>UserName</label>
<input name="txtUserName" type="text" value="ex@ex.com" id="txtUserName" onkeydown="DefaultButtonKeyPress(event, 'btnLogin')" />
<span id="rfvEmail" style="color:Red;display:none;">*</span>


What is the reason of script error ?


Thanks in advance