use tempdb
go
IF OBJECT_ID (N'dbo.fn_Alert') IS NOT NULL
    DROP FUNCTION dbo.fn_Alert
GO

CREATE FUNCTION dbo.fn_Alert(@alert_mask BIGINT)
RETURNS TABLE
AS RETURN
(
select @alert_mask as Mask
)
GO

SELECT * FROM dbo.fn_alert(0x4); -- this produces the expected result

DECLARE @T TABLE(alert_mask BIGINT)
INSERT INTO @T SELECT 0x4

select fn.mask, T.alert_mask from dbo.fn_alert(T.alert_mask) as fn
cross join @T as T
/* RESULT: 
Msg 4104, Level 16, State 1, Line 8
The multi-part identifier "T.alert_mask" could not be bound.
*/

DROP FUNCTION dbo.fn_Alert