First i would simplify the calculation on LOG_TIME, why do you cast every part to a string?
CAST((log_time (FORMAT 'hh:mi:ss')) AS CHAR(8)) AS HOUR_MIN_SEC
You might also avoid typecasting to a string:
log_time - ((EXTRACT(SECOND FROM log_time) MOD 1) * INTERVAL '1' SECOND)
Based on your query i'm not shure if you want the count per minute, then simply remove the "mod 1" (or change the FORMAT).
And then it's just a QUALIFY:
log_time - ((EXTRACT(SECOND FROM log_time) MOD 1) * INTERVAL '1' SECOND) AS HOUR_MIN_SEC,
COUNT(*) AS Downloads_Per_Second
WHERE LLNW_REDRCT_STAT_CODE IN ('DVR%20STATUS%3A%20DOWNLOAD_COMPL',' DOWNLOAD_COMPLETED')
AND LOG_DATE BETWEEN '2013-03-11' AND '2013-03-17'
--AND LOG_TIME < '09:00:00'
GROUP BY 1,2
OVER (PARTITION BY Log_Date, EXTRACT(HOUR FROM HOUR_MIN_SEC)
ORDER BY Downloads_Per_Second DESC) = 1
I just checked my query in SQLA and it only complained about the missing table :-)
I would expect this error when there was a type in COUNT(*), better check your query.