I have figured this out. It turns out that "configuring the datatree 
backend" is more than just creating the datatree tables for Horde.



This is the related documentation section of the Nag installation that 
was needed to resolve this problem.

5. Completing Configuration

1b. Configuring a DataTree backend

Can you direct me to the related documentation for configuring Horde's 
datatree backend? I am not sure if I did this step or not.

You still didn't answer my question about the datatree backend. In 
Horde's configuration.

I am do not have Kolab installed. I only have Horde, Kronolith, and 
Nag installed.

You don't happen to use Kolab?

Below is the list of tables I have created using the provided scripts. 
When I configured Nag, I chose Horde and Kronolith to be linked in 
Nag's menu.



horde=> \d

                    List of relations

  Schema |           Name            |   Type   | Owner

--------+---------------------------+----------+-------

  public | horde_datatree            | table    | horde

  public | horde_datatree_attributes | table    | horde

  public | horde_histories           | table    | horde

  public | horde_histories_seq       | sequence | horde

  public | horde_prefs               | table    | horde

  public | horde_sessionhandler      | table    | horde

  public | horde_tokens              | table    | horde

  public | horde_users               | table    | horde

  public | horde_vfs                 | table    | horde

  public | kronolith_events          | table    | horde

  public | kronolith_storage         | table    | horde

  public | nag_tasks                 | table    | horde

(12 rows)

Did you configure Horde's datatree backend?

When creating a New Task, and using any input, and click Save, I get 
this error message on the next screen:

Access denied saving task: No object requested.



There is no error in the web server logs.