Append query won't "run".

Now that you have some suggestions on how to do it, why bother?  You already have the data in tables de1 and 2.  What do you hope to accomplish with a 3rd table?

INSERT INTO de3

( PWS_ID, CCRYear, DateCCRDelivered, DateCCRReceived, DateCertLetterReceived, TNRCC_CCR, URL )

SELECT de2.PWS_ID, de2.CCRYear, de2.DateCCRDelivered, de2.DateCCRReceived, de2.DateCertLetterReceived, de2.TNRCC_CCR, de2.URL

FROM

(de1 INNER JOIN de2 ON (de1.URL = de2.URL) AND

(de1.TNRCC_CCR = de2.TNRCC_CCR) AND

(de1.DateCertLetterReceived = de2.DateCertLetterReceived) AND

(de1.DateCCRReceived = de2.DateCCRReceived) AND

(de1.DateCCRDelivered = de2.DateCCRDelivered) AND

(de1.PWS_ID = de2.PWS_ID) AND

(de1.CCRYear = de2.CCRYear))

LEFT JOIN de3 ON

(de2.TNRCC_CCR = de3.TNRCC_CCR) AND

(de2.URL = de3.URL) AND

(de2.DateCertLetterReceived = de3.DateCertLetterReceived) AND

(de2.DateCCRReceived = de3.DateCCRReceived) AND

(de2.DateCCRDelivered = de3.DateCCRDelivered) AND

(de2.PWS_ID = de3.PWS_ID) AND

(de2.CCRYear = de3.CCRYear)

WHERE

(((de3.PWS_ID) Is Null) AND

((de3.DateCCRDelivered) Is Null) AND

((de3.DateCCRReceived) Is Null) AND

((de3.DateCertLetterReceived) Is Null) AND

((de3.TNRCC_CCR) Is Null) AND

((de3.URL) Is Null) AND

((de3.CCRYear) Is Null));

I hope that helps.

You are probably not going to get a whole lot of suggestions unless you do post your code, since nobody has any idea what you are trying to do.

Phil