luya: Error 500 Internal Server Error in /admin/api-admin-menu

What steps will reproduce the problem?

$ composer create-project luyadev/luya-kickstarter:@dev
$ cd luya-kickstarter
$ cd configs
$ cp env.php.dist env.php
$ cp env-local-db.php.dist env-local-db.php
$ vi env-local-db.php
(configure DB connection for a PostgreSQL database)
$ cd ..
$ ./vendor/bin/luya migrate
$ ./vendor/bin/luya import
$ ./vendor/bin/luya setup

• Configure /etc/hosts and Apache virtualhost luya.local.
• Go to http://luya.local/admin and enter admin user credentials.

What is the expected result?

The admin page rendered without errors.

What do you get instead? (A Screenshot can help us a lot!)

A 500 (Internal Server Error) message.

If I go to http://luya.local/admin/api-admin-menu, I get the following XML output:

<response>
<name>Unauthorized</name>
<message>Your request was made with invalid credentials.</message>
<code>0</code>
<status>401</status>
<type>yii\web\UnauthorizedHttpException</type>
</response>

LUYA Check ouput (run this script and post the result: luyacheck.php)

1: [in_array('mod_rewrite', apache_get_modules())] true
2: [ini_get('short_open_tag')] ''
3: [ini_get('error_reporting')] '22527'
4: [phpversion()] '7.0.8-0ubuntu0.16.04.3'
5: [php_ini_loaded_file()] '/etc/php/7.0/apache2/php.ini'
6: [php_sapi_name()] 'apache2handler'

Q	A
LUYA Version	e2f7db7
PHP Version	7.0.8-0ubuntu0.16.04.3
Platform	Apache
Operating system	Ubuntu 16.04.1 LTS