Your design change for the specified store intersects with another one, please specify another date range.
You may get this error message while you try to change your template in magento . Even after setting the date range you might get the same error message. We have a work around for this :
Step 1 : Go to phpmyadmin and search for the table design_change
Step 2 : Edit the row from default/blank to your template say default/mynewtemplate