Rails - Nov 2005 - date_select helper error

I have this date select helper:

<%= date_select("customer", "dob", :include_blank =>
true, :order =>
[:month, :day]) %>

I get this error when posting the form:
1 error(s) on assignment of multiparameter attributes

The error happens when I take off the :year option.

Any clues as to why this maybe happening?

Serge