Group By error

Group By error

HI 
can you explain why the following doesn't work as a zoho query but works using raw SQL. 
Thanks
Joe



clientID,
sid,
`Activity Type : L1`,
min(`Date of activity`)
FROM opf_act
WHERE `Activity Type : L1` IN('Pathway referral', 'Other informal learning')
GROUP BY clientID;
It generates the following  error 
Inline images 1


If I add any of the other fields  to the Group By ,, then the table is no long a summary table.