Something I just noticed in case it helps you troubleshoot. When I type in the RadNumericTextBox in the popup, there's a javascript error:
_2.NumberFormat is undefined
I'm using the exact same RadNumericTextBox declaration that works for me everywhere else in my site:
<telerik:RadNumericTextBox ID="radQty" runat="server" Width="80px" Skin="MillenniumAdmin"
EnableEmbeddedSkins="false" DbValue='<%# Bind("Qty") %>' EnableViewState="true"
Type="Number">
<NumberFormat DecimalDigits="0" />
</telerik:RadNumericTextBox>
The javascript error happens on this line:
if(!_2.NumberFormat.AllowRounding){