Since we experience some troubles with binding a report to a data reader (especially in a web application) we would not recommend using it at this time. Rather, we would encourage you to use data sets or even easier - SqlDataAdapter. Since you are using the web viewer (you are developing a web application, correct?) and the report is rendered in HTML, you cannot count on the multicolumn functionality.
To learn more on the limitations of the different export formats please review this
topic in the online help documentation.
In case our suggestion does not help, please send us your reports so we can examine them and get back to you with a proper resolution. You can send us your reports in a formal support ticket.
the Telerik team