See, there is simple rule if objects present in your change list refer to any of the objects which doesn't exist or are locked/present in some other change list you will get RC=8 error.
In your case you can leave your change list open for now, first import the Business Component and activate its change list after that try to activate the existing change list.
In case if you still get the same error for non-existance of the business component then try to reject the change list and import your changes again.
Regards
Vj
