node->lnid not accesible from CCK computed field

I'm trying to use $node->lnid as a value for a CCK computed field. I have done this before in the 5.x version of the module but the same configuration doesn't work undex 6.x.
As a test, I've assigned "print_r($node)" to the value of the computed field and "lnid" attribute does not appear in the object.