An INSERT EXEC Statement Cannot Be Nested.

I try to select a store procedure in SqlExpress2005 which inside store procedure execute another store procedure,
When I select it but it prompt error messages "An INSERT EXEC statement cannot be nested.".
In Fire bird /Interbase store procedure we can nested. Below are the code;
declare @dtReturnData Table(doccode nvarchar(20), docdate datetime, debtoraccount nvarchar(20))
Insert Into @dtReturnData
Exec GetPickingList 'DO', 0, 37256, 'N', 'N', 'YES'
Select doccode, docdate, debtoraccount
From @dtReturnData
Inside the GetPickList It will do like this, but most of the code I not included;
ALTER PROCEDURE GETPICKINGLIST
@doctype nvarchar(2),
@datefrom datetime,
@dateto datetime,
@includegrn char(1),
@includesa char(1),
@includedata nvarchar(5)
AS
BEGIN
declare @dtReturnData Table(doccode nvarchar(20),
docdate datetime,
debtoraccount nvarchar(20))
IF (@DOCTYPE = 'SI')
BEGIN
Insert Into @dtSALESINVOICEREGISTER
Exec SALESINVOICEREGISTER @DateFrom, @DateTo, @IncludeGRN, @IncludeSA, @IncludeData
END
ELSE
BEGIN
Insert Into @dtDELIVERYORDERREGISTER
Exec DELIVERYORDERREGISTER @DateFrom, @DateTo, @IncludeGRN, @IncludeSA, @IncludeData
END
Select doccode,docdate,debtoraccount From @dtReturnData
END

So how can I select a nested store procedure? can someone help me