Convert the date column to FLOAT, then back to DATETIME:

DECLARE @test-2 TABLE (

dtColumn datetime

)

INSERT INTO @test-2 VALUES (GETDATE() + RAND())

INSERT INTO @test-2 VALUES (GETDATE() + RAND())

INSERT INTO @test-2 VALUES (GETDATE() + RAND())

INSERT INTO @test-2 VALUES (GETDATE() + RAND())

SELECT CAST(AVG(CAST(dtColumn AS FLOAT)) AS datetime)

FROM @test-2

Hope this helps

Gianluca