Correct code:
SET ANSI_WARNINGS OFF;
SELECT TOP 10000 Convert(DateTime,Floor(Cast((DateTime) as Float)),0) AS SummaryDate,
Nodes.Caption AS NodeName,
MAX(ResponseTime.MaxResponseTime) AS MAX_of_Peak_Response_Time,
MIN(ResponseTime.MinResponseTime) AS MIN_of_Minimum_Response_Time,
(MIN(ResponseTime.MinResponseTime) - MAX(ResponseTime.MaxResponseTime)) * (-1) AS Jitter
FROM
Nodes INNER JOIN ResponseTime ON (Nodes.NodeID = ResponseTime.NodeID)
WHERE
(
(Nodes.Customer = 'GIS') OR
(Nodes.Publicity = 'STM')
)
GROUP BY Convert(DateTime,Floor(Cast((DateTime) as Float)),0),
Nodes.Caption
ORDER BY SummaryDate ASC;