conditions array results in undefined


   I'm having another small problem. I run a small query to get all
the group_id's that are associated with a user. I then take that and
run it in another query in order to display the relevant data/group ID
the user belongs in. But when I do this, sometimes it returns an
error because there's 'nomethod' in array, and other times it returns
nothing. For example, this is my code...

  def list
    username = 'bob'
    resUser = User.find(:all, :conditions => ["username = :name",
{:name => username}], :select => "group_id")

    @result_pages, @results = paginate :results, :per_page =>
10, :conditions => ["group_id IN (?)", resUser]

In the logs, it does the first query, but for the second, it shows
  SQL (0.000314) SELECT count(*) AS count_all FROM results WHERE
(group_id IN (NULL))

That is true and that does work. But, users can belong to multiple
groups. So, for example, the table 'users' can look like this..

Username - Group_ID - Group
Bob - 1 - HR
Jim - 2 - OCF
Tim - 1 - HR
Mike - 3 - MED
Bob - 3 - MED

In the results table, a 'result' would belong to a group_id. So, if
'Bob' logs in, he should be able to view MED and HR results, but not
OCF. If I use the 'first' instead of 'all', then I only get the first
instance, which is 'HR'. I hope that makes sense.

Thank you again for any help!