GROUP BY And Text Field

SELECT OCRD.CardCode AS 'Customer No.', INV1.DocEntry as 'Doc En.', INV1.Text as 'Txt'
FROM INV1, OCRD
GROUP BY OCRD.CardCode, INV1.DocEntry, INV1.Text


This is the code that I expected to execute, but I am getting an error

When i put Text in the Group By its gives me an error
When i take Text out of the Group By it gives me an error

CardCode has numbers in it..DocEntry has numbers in it..Text has NULLs in it or blank values

Is there a way I can keep the group by and making this code work?

Any help is appreciated, thank you