Using 'ref' with variables in interface

In reply to dave_59:

When I say ‘called from outside’, I mean it is called from a class method.
task_fileio sends data to scoreboard through a queue which is unloaded in scoreboard
class.

I do not want to use anything other than task in order to reuse the task.
So, my question is, why cannot I connect an interface variable to a task ref value?