Fatal error: Call to undefined function array_fill_keys() in ...node_export_csv.module on line 53

I am trying to export to CVS format but I am getting this error:

Fatal error: Call to undefined function array_fill_keys() in /var/www/html/demo/sites/all/modules/node_export/modules/node_export_csv/node_export_csv.module on line 53

On the report page I noticed this warning:

warning: array_key_exists() [function.array-key-exists]: The second argument should be either an array or an object in /var/www/html/demo/sites/all/modules/node_export/modules/node_export_relation/node_export_relation.node_reference.inc on line 141.

I am using PHP 5.1.6 version...can anyone help?

Thanks

Ceci