Sql Query Error

Hi all, i wrote a sql statement by using a subquery, and on the subquery "(SELECT IssueID FROM UserIssue WHERE (UserName = @UserName)", it returns more than one IssueID, so I got the error likes "Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression. " How can I solve this problem? Thanks a lot.


<asp:SqlDataSource ID="IssueSQLDB" runat="server" ConnectionString="<%$ ConnectionStrings:ConnectionString %>"
                    SelectCommand="SELECT IssueID, DateOfIssue, DateOfRelease, DateOfUpload, CostOfCurrentIssue, IssueDesc FROM Issue WHERE (PublicationName = @PublicationName) AND (IssueID <> (SELECT IssueID FROM UserIssue WHERE (UserName = @UserName)))">
                    <SelectParameters>
                        <asp:ControlParameter ControlID="ddlPublication" Name="PublicationName" PropertyName="SelectedValue"
                            Type="String" />
                        <asp:SessionParameter Name="UserName" SessionField="loginName" />
                    </SelectParameters>
</asp:SqlDataSource>