Inner Join between 2 queries resulting in "Invalid Operation" - sql

Question

In an attempt to create a listing of Orders (each with multiple items) that satisfy some criteria, I have attempted to create a typical LEFT JOIN statement.
The attempt looks like this
SELECT
Q1.Order_Number,
OD.Item_Num
FROM
(
SELECT
OS.Order_Number
FROM
[4-Open_Order_Summary] AS OS
WHERE
Date() >= OS.Ship_Date AND
OS.Back_Ordered > 0
)
AS Q1
LEFT JOIN [1-Open_Order_Data] AS OD
ON Q1.Order_Number = OD.Order_Number
Running this query gives me an unexplained "Invalid operation" error. Researching this error with regards to Access SQL has led me to this question on StackOverflow pertaining to multiple JOIN statements of different types, and this question on the SuperUser branch pertaining to FULL OUTER JOIN statements. However I was unable to find questions related to a single LEFT JOIN statement.
In my attempts to resolve this I have done the following;
Changing
ON Q1.Order_Number = OD.Order_Number to
ON Q1.Order_Number LIKE OD.Order_Number
crashes Access
Running
SELECT
Q1.Order_Number,
FROM
(
SELECT
OS.Order_Number
FROM
[4-Open_Order_Summary] AS OS
WHERE
Date() >= OS.Ship_Date AND
OS.Back_Ordered > 0
)
AS Q1
returns the intended order numbers.

Answer 1

Why not try something like the following if you're trying to get Order Numbers from one table, and related Order Details from another?
SELECT
Q1.Order_Number
OD.Item_Num
FROM
[4-Open_Order_Summary] Q1
LEFT JOIN
[1-Open_Order_Data] OD
ON
OD.Order_Number = Q1.Order_Number
WHERE
DATE() >= Q1.Ship_Date
AND Q1.Back_Ordered > 0