Hi @Zitrone79
Sorry for the trouble you have faced but we are not facing or able to reproduce these issues at our end. We tried our local development sites, testing sites and even demo site but not able to reproduce them.
Do you have any working online site on which we can test this mysql error?
Fatal error: Cannot use object of type WP_Error as array in C:\xampp\htdocs\wordpress\wp-content\plugins\buddypress-media\app\main\controllers\media\RTMediaMedia.php on line 512
Please have a look at this line of code: https://github.com/rtCamp/rtMedia/blob/master/app/main/controllers/media/RTMediaMedia.php#L512. We have check for is_wp_error in very next line, so I don't think that this should be the case. Do you happen to have any custom changes in rtMedia or something? Can you check with the fresh WordPress setup once? Also check once with other plugins disabled and with WordPress default theme because it might be some plugin conflict or theme issue.
Regards.