Error message

• Notice: Undefined property: stdClass::$products in eval() (line 11 of /var/www/www.spectrumboeken.nl/sites/all/modules/contrib/ds/modules/ds_format/ds_format.module(66) : eval()'d code).
• Notice: Trying to get property of non-object in eval() (line 11 of /var/www/www.spectrumboeken.nl/sites/all/modules/contrib/ds/modules/ds_format/ds_format.module(66) : eval()'d code).