v7.6 and later
In the data model, there is a property on the Attachment field that you need to set to Public.
<sq:Grid runat="server" ID="grdFiles" CellSpacing="0" GridLines="None" DataSourceID="dsFiles"> <MasterTableView CommandItemDisplay="None" DataSourceID="dsFiles" AutoGenerateColumns="False"> <RowIndicatorColumn Visible="True"></RowIndicatorColumn> <ExpandCollapseColumn Visible="True"></ExpandCollapseColumn> <Columns> <sq:GridHyperLinkColumn DataNavigateUrlFields="fldIActId,FileRefValue" DataNavigateUrlFormatString="/_layouts/ViewFile.aspx?activityInstanceId={0}&fileid={1}" DataTextField="FileRefText" DataTextFormatString="{0}" Text="Attachment" AllowSorting="False" HeaderText="Attachment" UniqueName="Attachment"> </sq:GridHyperLinkColumn> </Columns> </MasterTableView> </sq:Grid>