[Antivirus]

I don't think you can use vfmethod for custom fields added to datamanagers unless a function already exists. I get around this problem by checking validation using php like follows:

PHP Code:

'daysprune'         => array(TYPE_INT,        REQ_AUTO, 'if ($data == 0) { $data = -1; } return true;'), 


There's some good details on datamanagers here, but I assume you've already read that.