feoDownload: Attempt to set NOT NULL field referer to NULL

Always getting this error:

[2012-04-26 13:58:58] (ERROR @ /index.php) feoDownload: Attempt to set NOT NULL field referer to NULL

On MODX Revolution 2.2.1-pl (traditional)
MySQL 5.1.61
Php 5.2
Host: Bluehost

Anyone?

Same here ...

[2012-05-20 10:43:57] (ERROR @ /index.php) feoDownload: Attempt to set NOT NULL field referer to NULL

MODX Revolution 2.2.1-pl (traditional)
Database: 5.1.41-3ubuntu12.10
PHP Version 5.2.17

I can´t figure out what is causing this ...

Has anyone seen this before?

Best regards
Micke