Raspberry Pi 3 Model B Plus, Ubuntu Mate installation error: "driver 'sdhost-bcm2835' already registered, aborting




I've just bought me a new Raspberry Pi 3 Model B Plus and wanted to install Ubuntu Mate on it.
So I cleared my SD-Card with the "SD Card Formatter", downloaded Ubuntu Mate from https://ubuntu-mate.org/raspberry-pi/ubuntu-mate-18.04.2-beta1-desktop-armhf+raspi-ext4.img.xz and installed it onto my SD-Card with "Win32DiskImager".
But when I plugged the card in and turned on the power of my Raspberry Pi, I got the following on my screen:

[  Runtime] Driver 'sdhost-bcm2835' already registered, aborting...
[  Runtime] EXT4-fs (mmcblk0p2): error loading journal

BusyBox v1.27.2 (Ubuntu 1:1.27.2-2ubuntu3.1) built-in shell (ash)
Enter 'help' for a list of built-in commands.


I've been looking for a solution for hours now and only found one really confusing post, so any help would be appreciated. ; D
Thanks in advance.