Alias Woes

so, I have created a working SQL statement that summarises data from a bunch of different tables (it's a stock monitoring application so it all has to do with levels of stock, numbers of parts processed etc...):

SELECT tblPPIn.BatchID,
tblPartDescriptions.DrawingNumber AS [Drawing Number],
tblOrder.IssueNumber AS [Issue Number],
tblPartDescriptions.Description AS [Description],
tblPPIn.Qty AS [Total Booked In],
IIf(IsNull((SELECT Sum(tblPPProcessed.QtyProcessed) AS SumOfQtyProcessed FROM tblPPProcessed WHERE tblPPProcessed.BatchID = tblPPIn.BatchID;)),'0',(SELECT Sum(tblPPProcessed.QtyProcessed) AS SumOfQtyProcessed FROM tblPPProcessed WHERE tblPPProcessed.BatchID = tblPPIn.BatchID;)) AS [Total Qty Processed],
IIf(IsNull((SELECT Sum(tblPPOut.Qty) As sumofQtyOutPass FROM tblPPOut WHERE tblPPOut.BatchID = tblPPIn.BatchID AND tblPPOut.IQCPass = 'PASS';)),'0',(SELECT Sum(tblPPOut.Qty) As sumofQtyOutPass FROM tblPPOut WHERE tblPPOut.BatchID = tblPPIn.BatchID AND tblPPOut.IQCPass = 'PASS';)) AS [Total Good Parts Taken],
IIf(IsNull((SELECT Sum(tblPPOut.Qty) As sumofQtyOutUninspected FROM tblPPOut WHERE tblPPOut.BatchID = tblPPIn.BatchID AND tblPPOut.IQCPass = 'UNINSPECTED';)),'0',(SELECT Sum(tblPPOut.Qty) As sumofQtyOutUninspected FROM tblPPOut WHERE tblPPOut.BatchID = tblPPIn.BatchID AND tblPPOut.IQCPass = 'UNINSPECTED';)) AS [Total Uninspected Parts Taken],
IIf(IsNull((SELECT Sum(tblPPProcessed.QtyPass) AS SumOfQtyPass FROM tblPPProcessed WHERE tblPPProcessed.BatchID = tblPPIn.BatchID;)),'0',(SELECT Sum(tblPPProcessed.QtyPass) AS SumOfQtyPass FROM tblPPProcessed WHERE tblPPProcessed.BatchID = tblPPIn.BatchID;)) AS [Total Passes],
IIf(IsNull((SELECT Sum(tblPPProcessed.QtyFailEtching) + Sum(tblPPProcessed.QtyFailCutOut) + Sum(tblPPProcessed.QtyFailFlatness) + Sum(tblPPProcessed.QtyFailHandling) + Sum(tblPPProcessed.QtyFailOther) AS SumofFails FROM tblPPProcessed WHERE tblPPProcessed.BatchID = tblPPIn.BatchID;)),'0',((SELECT Sum(tblPPProcessed.QtyFailEtching) + Sum(tblPPProcessed.QtyFailCutOut) + Sum(tblPPProcessed.QtyFailFlatness) + Sum(tblPPProcessed.QtyFailHandling) + Sum(tblPPProcessed.QtyFailOther) AS SumofFails FROM tblPPProcessed WHERE tblPPProcessed.BatchID = tblPPIn.BatchID;))) AS [Total Fails],
[Total Booked In]-[Total Qty Processed]-[Total Uninspected Parts Taken] AS [Total Unprocessed Parts Remaining],
[Total Passes]-[Total Good Parts Taken] AS [Total Good Parts Remaining],
[Total Passes]/[Total Qty Processed] AS [Overall Yield]
FROM tblPPIn INNER JOIN (tblPartDescriptions INNER JOIN tblOrder ON tblPartDescriptions.DrawingNumber = tblOrder.DrawingNumber) ON tblPPIn.BatchID = tblOrder.BatchID
ORDER BY tblPPIn.BatchID ASC;

don't worry about the details, it works as it is above...

now I only want to display data for batches where there are some parts left, so I've tried adding the following WHERE clause:

WHERE ([Total Good Parts Remaining] + [Total Unprocessed Parts Remaining]) <> 0

should work fine, right?
nope, we get the (all too familiar) 'Enter parameter value: Total Good Parts Remaining' (and the same for 'Total Unprocessed Parts Remaining'), despite the fact I have used these aliases in the previous SQL with no problem...

Is there any way around this or do I have to create a big-ass WHERE statement complete with the subqueries I've already used previously?

This is seriously annoying me today... any help would be massively appreciated!

cheers,
Bogzla