"Empty needle" error when exporting from Advanced Search results
It's likely an issue with the code. The fastest "fix" is to hide that armless message by changing the setting. you add in your civicrm.setting.php that line:

ini_set("error_reporting", 0);


and it should avoid to show that message.

Beware that it means that you might have other errors (eg. from other modules) that will be hidden too.