obviously the error says one of your subquery is return more than one result
Seems one of your table does not have a primary key
so you have do the following steps
just check the following queries
select Client_name, Count(*) from tblClient
Group by Client_name
Having count(*)>1
select Supplier, count (*) from tblProductSupplier
Group by Supplier
Having count(*)>1
select [Group], count (*) from tblProduct_Group
Group by [Group]
Having count(*)>1
select Period , count (*) from tblWarrantyPeriod
Group by Period
Having count(*)>1
if any of the above query return results then you need to check the data in that table
(keep it in mind i have just give you a way to solve this issue)
i feel the first query return results in that case try to recreate the query with clientid instead of client name in your query
like this
(select ClientID from tblClient where ClientID = sm.Clientid)
Hope you understand ;)