In both of them you're mixing character & numeric data joined by +.

You need to CAST/CONVERT it all to character.

What data type are [BU], [SUBSIDUARY] & [OBJECT]?

CASE

WHEN [ORDER_TYPE] = 'SS' or [ORDER_TYPE] = 'SP'

THEN CAST([BU] AS VARCHAR(10)) + '.' + CAST([OBJECT] AS VARCHAR(10))

ELSE

CAST([BU] AS VARCHAR(10)) + '.'+ '14350' + '.' + CAST([SUBSIDIARY] AS VARCHAR(10))

END

Like this for instance:

declare @a as table ([BU] Varchar(10), [ORDER_TYPE] Char(2), [SUBSIDIARY] Varchar(10), [OBJECT] Varchar(10));

insert @a values ( 'BU1', 'SS', 'Slumpco', 'OBJECT1' );

insert @a values ( 'BU2', 'AA', 'Slumpco2', 'OBJECT2' );

select

CASE

WHEN [ORDER_TYPE] = 'SS' or [ORDER_TYPE] = 'SP'

THEN [BU] + '.' + [OBJECT]

ELSE

[BU] + '.'+ '14350' + '.' + [SUBSIDIARY]

END

from @a