Query Returning #error When It Should Be Null

I have a left-join query where I know that some of the values in the left-hand table have no corresponding values in the right-hand table...that's why I used a left-join: I want all the values in the left-hand table to show up. I would expect that records without corresponding values in the right-hand table would show up as nulls (I swear I have dozens of other queries that work this way) but in this one, they show up as "#error" instead.

This is a problem because I want to do some calculations on this field. Normally I would use the nz function to change the nulls to zeros.

So,
1. Any idea why this is happening?
2. Is there a way to change the #error values to zeroes, similar to using the nz function?

HEre's the SQL:
SELECT FeederInventorySummary.machine, FeederInventorySummary.Size, FeederInventorySummary.Leaf, FeederInventorySummary.Type, FeederInventorySummary.CountOfFeederID,FeederNeeds Summary_7.FeederQty FROM FeederInventorySummary LEFT JOIN FeederNeedsSummary_7 ON (FeederInventorySummary.Type = FeederNeedsSummary_7.Type) AND (FeederInventorySummary.Leaf = FeederNeedsSummary_7.Leaf) AND
(FeederInventorySummary.Size = FeederNeedsSummary_7.FeederSize) AND (FeederInventorySummary.machine = FeederNeedsSummary_7.ActualMachine);

For every record without a corresponding record in FeederInventorySummary_7, the FeederQty field shows up

as #error.