An issue with theme selector

I recently upgraded my Moodle from 1.9 to 2.2 and then to 2.3.2. Now I'm having a problem with the theme selector. When I go to Site administrator --> Appearance --> Themes --> Theme Selector and try to change my current (Device type: Current) theme, Moodle just takes me to the empty page (with the address like: http://moodle's address/theme/index.php?device=default&sesskey=8VmrvMbSgE) so I can't change my default theme.