Fehler: Aggregatfunktion

[Danfix]

query = "SELECT total=SUM(Tabelle1.Test) FROM Tabelle2, Tabelle1 "
query = query & "WHERE Tabelle1.session_id='" & sessionid & "'"
RS.Open query, nameConn

SELECT SUM(Tabelle1.Test) AS Total FROM Tabelle2, Tabelle1
WHERE Tabelle1.session_id= sesionid ;