How to modify the workflow of sub-task?

[Karmen Cheung]

I have tried to modify the workflow of sub-task which is copy from the workflow of other issue from the same project, but it gives me an error of "Statuses can't be removed from active workflows" and it said I only can remove the statuses from inactive workflows. If made the original workflow inactive and it will affect the original workflow. So, what could I do for modifying the workflow of sub-task without affecting the original workflow of issue?

[Phill Fox]

The way to solve this problem is to take a copy of the workflow that is currently used for your subtasks.

Amend this copy by changing statuses/transitions as appropriate.

Then copy the workflow scheme that was originally in use.

Swap the workflow associated with subtasks to your new workflow. 

Apply the new workflow scheme to all the projects that should use the modified flow. 

(If the original workflow was the default and you want future projects to automatically get this flow then do these extra steps.)
Once all projects are associated with the new workflow scheme your original workflow scheme will be inactive. Swap the workflow associated with subtasks.