Linq Subquery not working

Hi,

I am trying to create a linq query which contains a few subqueries. The query I have created seems to be correct (at least, in syntax) but I get no data sent back and Fiddler is showing an error with this query:

        public IQueryable<vGatekeeperApproval> GetGatekeeperApprovals(string UserName)
        {
            SystemsFormsDataContext db = new SystemsFormsDataContext();
            IQueryable<vGatekeeperApproval> query;

            Int32 UserId = GetCurrentUserId(UserName);
            bool IsGatekeeperApprover = IsCurrentUserGKApprover(UserName);
            string strSysApproverEmail = GetSystemsApproverEmail(UserName);

            try
            {
                query = (from s in db.vGatekeeperApprovals
                         join r in db.Requests on s.RequestId equals r.Id
                         where (IsGatekeeperApprover == true || s.OverrideApproverId == UserId)

                         && (
                         (
                         from u in db.Staffs
                         where u.GateKeeperArea == 
                            (from c in db.vGK_DIV_USING_CCs 
                             where c.SEGMENT_CODE ==
                                (from a in db.Attributes
                                 where a.AttributeItemId== global_COSTCENTRE && a.FormId==s.Id
                                 select a.AttributeValue).FirstOrDefault()
                             select c.PARENT_CODE_L3 
                             ).FirstOrDefault()
                         select u.Id
                         
                         ).ToList().Contains(UserId)

                         )

                         select s
                          );
 

            }
            catch (Exception ex)
            {
                query = (from s in db.vGatekeeperApprovals
                         where s.UserId == 0
                         select s);

                //LogEvent("ERROR!" + ex.Message, ex.Source);
            }

            return query;
        }

Any ideas what is causing the problem? Is there a better way to create a subquery in linq?

Any help would be greatly appreciated.

Shuja