The roles "Owner", "Publishing Author", and "Publishing Editor" cannot be assigned to a user for the Public Folder in POA Customer CP.
Activation parameter "Allow creation of subfolders under Public Folder via OWA and Outlook" is set to "Disallow" in the service template which the subscription is based on. All roles with "CreateSubfolders" permission are disabled in POA Customer CP if this setting is set to "Disallow."
Change this activation parameter to "Allow" in the "Parameters" tab for the service template the problem subscription is based on. This will affect all subscriptions for all service plans based on that service template. Changing the parameter for just one subscription is not possible. Once the activation parameter is changed, it will become possible to assign the roles "Owner", "Publishing Author", and "Publishing Editor" using POA Customer CP.