Using elemnts with CCK fields

Hi,

I'm trying to use elements fields on a CCK field, in a hook form alter I change the type of the field to emailfield, but when the form is submitted I see this error:

Fatal error: Only variables can be passed by reference in /home/www/htdocs/moflow/moflow-1.2/includes/form.inc on line 1351

I think is related with form_set_values function and the way that CCK manage fields.

Any ideas?.