Open addproducts.ascx located in the \desktopmodules\smith.buynow folder and go to line 560 and you will see the following line of code. Just add a space after the "d" as hightlighted below:
<asp:RegularExpressionValidator ID="rgvVariantGroup" runat="server" ErrorMessage="Enter only letters and numbers"
ValidationExpression="^[a-zA-Z\d ]+$" ControlToValidate="txtProductVariantGroup" Display="Dynamic"/>
We have updated this in the latest build.
-Scott