Group by within table joins

Hi, I have the following SQL:

SELECT ltb.v_id,
       count(ltb.v_id) AS num_of_times_borrowed,
       vtb.equip_attr[1] AS year,
       vtb.equip_attr[3] AS model,
       vtb.equip_attr[4] AS type
FROM log_tb ltb, vehicle_tb vtb
WHERE ltb.v_id=vtb.equip_id
GROUP BY ltb.v_id
ORDER BY year;

"ERROR: Attribute vtb.equip_attr must be GROUPed or used in an aggregate
function"

but, it didn't work.  I want to know how many time each vehicle has been
borrowed. Please help.  Thanks.


- Bernie