Redmine

Hello,

I'm trying to give one of my user groups the capability to add subtasks to issues that are assigned to a specific person, but to prevent the "New Issue" capability.
My problem is, that if I give them the "Manage Subtask" capability, they see within the issue overview the "Add" in the subtask line, but after clicking it, they get a Error message: "403 - You are not authorized to access this page.".
After I allow them to also add "New issues" they are able to add subtasks without error message, but have also the capability to add new issues.

Is there a way to allow to add subtasks and to prevent adding new issues?

Thanks
Kasia