Cannot delete auto generated policies after 2.4 upgrade
This access policy is still referenced by at least one Password, File or Session Request or ISA Password or File release. It cannot be deleted until the associated data ages out of the system.
Access Policies that are marked as "System" cannot be deleted, only disabled. However, any policy that is not a "System" policy, can be deleted after it is disassociated from all systems and accounts.
If you received the error stated above, then the Policy in question must be a System policy or it is still tied to an Account, or it is has a related request that is still active.