Runtime Error in component "EnsEMBL::Web::Component::Help::ListEnsemblMappings [content]"

Function EnsEMBL::Web::Component::Help::ListEnsemblMappings fails to execute due to the following error:

	Can't call method "slice" on an undefined value at
	... /ensemblweb/vega_archive/vega_68/sanger-plugins/vega/modules/EnsEMBL/Web/Component/Help/ListEnsemblMappings
	... .pm line 72.