>>
>>99% 10 records,
>>but in rare cases can be 10,000.
>>The procedure performs one operation of the operator ( save document ),
>>then pay price microsecond almost always
>>and gain a few seconds in the worst case improves
>>his experience in the use of the application.
>
>Can you post the code? I didn't see the code in the screen shot. Maybe I am missing something here.

....
DECLARE @DO_R TABLE (	id_#DO_R		INT	PRIMARY KEY
		,	id_DO_R			INT  -- PRIMARY KEY  works here !!!
		,	l_MA_Carico_Old	SMALLINT	)

	MERGE dbo.DO_R U
	USING (SELECT	#DR._action ... ) S
...
	OUTPUT INSERTED.id
		,	S.id
		,	CASE WHEN	DELETED.d_Movimento IS NOT NULL
					AND ISNULL(DELETED.l_MA_Dare,0)<>ISNULL(INSERTED.l_MA_Dare,0)
				THEN ISNULL(DELETED.l_MA_Dare,0)
			END	-- 0 indica il NULL NULL indica che dare non è il nuovo avere
		INTO @DO_R 
		(	id_DO_R
		,	id_#DO_R
		,	l_MA_Carico_Old
		);
...

the error occurs at compile time.

On the same procedure, (2000 lines),
there are others table variables with primary key and merge,
and they work!