The server principal "sa" is not able to access the database under the current security context

I'm working with SQL Server 2012 Express.

I'm using Service Broker to run a stored procedure asynchronously.

The activation procedure has to access another database to execute another stored procedure. This is the code:

CREATE PROCEDURE [dbo].[GetNewCodes]
        @gintNewCodes bigint,    
        @presNewCodes tinyint,
        @levelNewCodes bigint,
        @quantityNewCodes smallint
    AS
        -- Get new codes from INCIC database.
        DECLARE    @return_value int,
                @xmlGenerated xml,
                @xmlString NVARCHAR(MAX)
        SET NOCOUNT ON;
            -- Set that this stored procedure is running
            update dbo.RunningSPs with (serializable) set conf_value = 1
            where sp_name = N'GetNewCodes'
            if @@rowcount = 0
            begin
                insert dbo.RunningSPs(sp_name, conf_value) values (N'GetNewCodes', 1)
            end
        EXEC    @return_value = [INCIC].[dbo].[ReadCodeBuffer]
                @gint = @gintNewCodes,
                @pres = @presNewCodes,
                @level = @levelNewCodes,
                @quantity = @quantityNewCodes,
                @xmlGenerated = @xmlGenerated OUTPUT
        SET @xmlString = cast(@xmlGenerated as nvarchar(max))
        -- Process these new codes on TRZ.
        EXEC dbo.ProcessCodes @XmlString = @xmlString
        -- Update that we are not running this procedure any more.
        update dbo.RunningSPs with (serializable) set conf_value = 0
        where sp_name = N'GetNewCodes'
        if @@rowcount = 0
        begin
            insert dbo.RunningSPs(sp_name, conf_value) values (N'GetNewCodes', 0)
        end

The problem is here: [INCIC].[dbo].[ReadCodeBuffer], and the error message is:

Error: 50000   
Unrecoverable error in procedure GetNewCodes: 916: The server principal "sa" is not able to access the database "INCIC" under the current security context.

I have followed this tutorial to implement Service, queue and activation stored procedure.

How can I fix this problem?