Runtime Error in component "EnsEMBL::Web::Component::Gene::Summary [content]"

Function EnsEMBL::Web::Component::Gene::Summary fails to execute due to the following error:

	Can't call method "display_xref" on an undefined value at
	... /nfs/public/release/ensweb/live/www/www_111/ensembl-webcode/modules/EnsEMBL/Web/Component/Summary.pm line
	... 199.