Msg 512, Level 16, State 1, Procedure track_order1, Line 8 Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as...

Further to Solution 1 ... where ArunRajendra is exactly right in describing the approach you should take to finding the problem...

Most of your sub-queries are returning sum of something ... except this one

(Select distinct(volumn) from  Stock_Dispatch  where inst_id=@insid and PIid=@piid and title= pd.title) As Volumn

... which I suspect is the cause of your problem.

Another way you can make life easier for yourself is to use whitespace ... spaces, tabs, newlines ... this is your unaltered code reformatted with some whitespace to make it more readable ...

ALTER procedure [dbo].[track_order1]
@grnid int,
@insid int,
@piid int
as
begin
	Select distinct pii.inst_id, pd.PIid, pd.title,pd.publisher,pd.format ,pd.subscription_period_from as Sub_from,	pd.subscription_period_to as sub_to,pd.Qty_in_year AS Frequency	,
	(
		Select distinct(volumn) 
		from  Stock_Dispatch  where inst_id=@insid and PIid=@piid and title= pd.title
	) As Volumn,
	Coalesce(
	(
		Select Sum(cast(Dispatch_Qty  as int)) from dbo.Stock_Dispatch where inst_id=@insid and PIid=@piid 
		and title= pd.title and order_Status=2
	) ,0)as Rec_qtys,
	pd.Qty_in_year - Coalesce(
	(
		Select Sum(cast(Dispatch_Qty  as int)) 
		from dbo.Stock_Dispatch where inst_id=@insid and PIid=@piid and title= pd.title and order_Status=2
	) ,0) as rem,
	
	Coalesce(
	(
		Select Sum(cast(Dispatch_Qty  as int)) from 
		dbo.Stock_Dispatch where inst_id=@insid and PIid=@piid and title= pd.title and order_Status=1
	),0) as New_dispatch,
	case pd.Qty_in_year - Coalesce(
	(
		Select Sum(cast(Dispatch_Qty  as int)) 
		from dbo.Stock_Dispatch where inst_id=@insid and PIid=@piid and 
		title= pd.title and order_Status=2
	) ,0) 
	when 0 then 'Complete'
	else 'Not Completed' end as Order_stat

	from  
		dbo.Performa_details pd, 
		Client_Goods_details_master po,
		Stock_Dispatch sd 
		right outer join Performa_details pdio on pdio.PIid=sd.PIid,
		Performa_invoice pii 

	where po.PIid=pd.PIid and pd.PIid=pii.PI_id and Grnid=@grnid and pii.inst_id=@insid
end

Once I had done that it was very easy to spot the difference in the sub-queries.
I also notice that you have a mix of methods of joining tables. My advice would be to be consistent - I personally prefer to use ON clauses as it makes it easier to see what the actual filter being used is and also to spot any errors. I had an attempt at your from clause

from
    dbo.Performa_details pd
    inner join Client_Goods_details_master po on po.PIid=pd.PIid
    Stock_Dispatch sd, 
    right outer join Performa_details pdio on pdio.PIid=sd.PIid,
    inner join Performa_invoice pii on pd.PIid=pii.PI_id
    where Grnid=@grnid and pii.inst_id=@insid

and couldn't see how Stock_Dispatch was linked to the other tables (other than Performa_details)