SQL Count in Where clause

SQL Count in Where clause

I'm trying to find items that have shown up one time or less on a report.
I know that to find how many times each item has apepared, I use this.
select COUNT(VP.VendorPartID)
from Purchasing.PurchaseOrder PO with (nolock)
inner join dbo.tblVendor V with (nolock)
on PO.VendorID=V.VendorID
inner join Purchasing.PurchaseOrderItem POI with (nolock)
on PO.PurchaseOrderID=POI.PurchaseOrderID
inner join Purchasing.VendorPart VP with (nolock)
on POI.VendorPartID=VP.VendorPartID
where V.ProductTypeID=4
group by PO.PurchaseOrderID
But I tried to nest it within another query to be able to set that it must
appear 1 time or less, and it says there's an error because
"Subquery returned more than 1 value. This is not permitted when the
subquery follows =, !=, <, <= , >, >= or when the subquery is used as an
expression."
I did this, which I'm guessing is likely pretty wrong, haha.
select VP.VendorPartID,VP.VendorPartDescription
from Purchasing.PurchaseOrder PO with (nolock)
inner join dbo.tblVendor V with (nolock)
on PO.VendorID=V.VendorID
inner join Purchasing.PurchaseOrderItem POI with (nolock)
on PO.PurchaseOrderID=POI.PurchaseOrderID
inner join Purchasing.VendorPart VP with (nolock)
on POI.VendorPartID=VP.VendorPartID
where (
select COUNT(VP.VendorPartID)
from Purchasing.PurchaseOrder PO with (nolock)
inner join dbo.tblVendor V with (nolock)
on PO.VendorID=V.VendorID
inner join Purchasing.PurchaseOrderItem POI with (nolock)
on PO.PurchaseOrderID=POI.PurchaseOrderID
inner join Purchasing.VendorPart VP with (nolock)
on POI.VendorPartID=VP.VendorPartID
where V.ProductTypeID=4
group by PO.PurchaseOrderID
) < 2
group by VP.VendorPartID,VP.VendorPartDescription