It's not an error, it's only an information that you have a port with a default value set to ERROR('transformation error'), so Integration Service will skip the NULL values with an ERROR function.
The Designer inserts this expression automatically, when you add a new output port; you can change it. Edit the expression, find the port on the Ports tab and check the Default value field at the bottom:
The ERROR function causes the Integration Service to skip a row and issue an error message, which you define.