Error Please Help - Important

Hello,

When I try to run the following query:

if (select REQUEST from TEST_REPORT.dbo.TEAM3B_PULL_TOTAL_TST) Not In(select REQUEST from TEST_REPORT.dbo.REQUEST_BUS_REQ_TST)
begin
Insert into TEST_REPORT.dbo.REQUEST_BUS_REQ_TST (b.request,b.business_req_id,b.bus_test,b.test_cas e_id,b.test_case_source,b.test_case_descr)
select a.request,a.business_req_id,a.bus_test,a.test_case _id,a.test_case_source,a.test_case as test_case_description
from TEST_REPORT.dbo.TEAM3B_PULL_TOTAL_TST AS A INNER JOIN TEST_REPORT.dbo.REQUEST_BUS_REQ_TST AS B ON A.REQUEST = B.REQUEST
Order by REQUEST,BUSINESS_REQ_ID,TEST_CASE_ID
end

I am getting the error messages of:

Ambiguous column name 'REQUEST'.
Ambiguous column name 'BUSINESS_REQ_ID'.
Ambiguous column name 'TEST_CASE_ID'.

What is wrong in the above statement?

Thank you,