Non-admin users are not able to release items in the To Do List that have been set to "Any user".
Log into Pilot as a non-admin user. Launch a Wait for Action (Checkpoint) task on a file, with To set to "any user". Open the To Do List and select the entry that shows up in there. The Release button is grayed out. If you make that user as Admin, then the Release button is no longer grayed out.