Functions in SQL 2008

CREATE FUNCTION GetClientName
(
    @JobId bigint
)
RETURNS VARCHAR(MAX)
AS
BEGIN
    DECLARE @ClientName AS VARCHAR(MAX)
    select @ClientName = c1.clientname FROM tbl_client c1
    INNER JOIN tbl_mechanicalbrief m ON m.clientid = c1.clientid
    WHERE mechanicalid = @JobId
    Union
    select @ClientName = c2.clientname FROM tbl_iteration i
    INNER JOIN tbl_client c2 ON i.clientid = c2.clientid
    WHERE iterationid = @JobId
    Union
    select @ClientName = c3.clientname FROM tbl_release r
    INNER JOIN tbl_client c3 ON r.clientid = c3.clientid
    WHERE releasingid = @JobId
    RETURN @ClientName
END

Select statements included within a function cannot return data to a client.