sql query eror The multi-part identifier "first.course" coul

Question

 My query as follows

select First.course,second.Certificate_No,second.Issue_Authority,second.Issue_Date

from

(select distinct Course = case cr.cpm_pkg_id WHEN '' THEN cr.cmn_minor_code else cbm.cmn_minor_code end

from course_registration cr, batch_course_registration bcr, co_batch_master cbm where

bcr.cr_bill_no = cr.cr_bill_no and cbm.cbm_batch_id = bcr.bcr_batch_id and cr.cr_active = 'A' and

cr.stud_id = '9917') as first

left join

(select distinct b.courseelg,b.coursename,a.pm_prof_code as Code,a.sp_cert_no as Certificate_No,

a.sp_issu_authority as Issue_Authority, convert(char(14),a.sp_issu_dt,106) as Issue_Date from student_professional a,tb_courseelg_settings b

where a.pm_prof_code= b.courseelg and first.course = b.coursename and a.stud_id = '9917' ) as second

ON(second.coursename=first.Course)

 

When i run the above query shows error as follows

The multi-part identifier "first.course" could not be bound.