Contribution Summary (Donor Summary) Report problem with displaying name

When trying to create a Contribution Summary report (formerly called a Donor Report) and grouping by receive date, CiviCRM is not allowing the display of Contact Name, despite allowing the display of street address, zip code, and other related data.

This is the error message:
"Please correct the following errors in the form fields below:
Please do not use combination of Receive Date and Contact Name"

The following fields were checked: under Display Columns- Contact Name, Street Address. Under Group by Columns- Contact Name, Receive Date (year).

There is no problem if, under Display Columns, Contact Name is not displayed.

This is a link to where the error was happening on the demo site: http://drupal.demo.civicrm.org/civicrm/report/instance/6