> If you are using TIBQuery then you are using IBX.

OK, gotcha! I never knew this and really think I should have!
For that matter (as far as IBX is concerned) I'm using D6, sp2

NB: The mis-placed AS in the join in my first post was a typo.

Thanks for some great clarifying tips.
I have neatened up my queries, but...
grrr...
Same 2 errors

I will paste the actual query directly.
I must be missing something...

SELECT P.PTI_ID AS ID, // int
CAST('PTI' AS VARCHAR(10)) AS CAT,
P.BOXNUM AS BOXNUM, // domain, VarChar12
P.REFNUM AS REFNUM, // domain, VarChar16
P.PTIDATE AS JOBDATE, // DATE
CP.NAME AS CLIENT,
SP.NAME AS STATE
FROM PTI P
LEFT JOIN CLIENT CP ON (P.CL_ID = CP.CL_ID)
LEFT JOIN STATES SP ON (P.ST_ID = SP.ST_ID)
WHERE P.BOXNUM CONTAINING 'MMSF'
UNION
SELECT B.BD_ID AS ID, // int
CAST('Breakdown' AS VARCHAR(10)) AS CAT,
B.BOXNUM AS BOXNUM, // domain, VarChar12
B.REFNUM AS REFNUM, // domain, VarChar16
B.BDOWNDATE AS JOBDATE, // DATE
CB.NAME AS CLIENT,
SB.NAME AS STATE
FROM BDOWN B
LEFT JOIN CLIENT CB ON (B.CL_ID = CB.CL_ID)
LEFT JOIN STATES SB ON (B.ST_ID = SB.ST_ID)
WHERE B.BOXNUM CONTAINING 'MMSF'
ORDER BY 1, 3

I have checked all the fields, and they are all same datatype/size
(most are domains) - indicated above after comment//

I'm still getting the problem though...

The next thing I guess I will try is to explicitly CAST each field so
I KNOW they are the same in both sets.
(Even though I know they are as the fields come from the same domains)
I will try this tomorrow morning.
I'm going batty-blind from trying to sort this out for the last 5 hours...

Thanks again for your help (always appreciative)

Kind regards,
-Ryan