Stored Procedure Error converting data type nvarchar to int.

I created the following stored procedure:
CREATE PROCEDURE spGetMarkup
@CustomerID int,
@OriginCountryID int,
@DestinationCountryID int,
@ServiceID int,
@PackageTypeID int,
@Markup int OUTPUT
AS

SELECT @Markup =(Markup)
FROM tblMarkups
WHERE (CustomerID = @CustomerID) AND
            (OriginCountryID = @OriginCountryID) AND
            (DestinationCountryID = @DestinationCountryID) AND
            (ServiceID = @ServiceID) AND
            (PackageTypeID = @PackageTypeID)

I get the error when when executing.  "Error converting data type nvarchar to int".    All fields in the table are int datatype.

DECLARE @Markup int
EXECUTE spGetMarkup @CustomerID = 124001, @OriginCountryID = OriginCountryID, @DestinationCountryID = DestinationCountryID, @ServiceID = ServiceID, @PackageTypeID = PackageTypeID, @Markup = @Markup OUTPUT
SELECT @Markup