Call to a member function get() on null - Windows 10

Im getting error "Call to a member function get() on null" after downloading themes. It seems that "$this->dateFormat = $this->config->get('plugins.datetools.dateFormat.default');" in construct function returns null. Graverror

Update: using grav version 1.1.1 + xamp + php 5.6.23

I now tried to install grav core only and install the admin panel afterwards and now everythin works fine. Before I directly installed grav core + admin which lead to the exception. This issue can be closed now.