Graphic error on VisualBoyAdvance

[hencelence]

Hey there,

this is probably an easy fix, but I can't find the solution.
I'm trying to play pokemon firered as .gba-ROM on the VisualBoyAdvance v1.8.0 that I got via software center.
Sound and speed work just fine, but the graphics keep on glitching (see image attached).
I tried with a few other .gba-roms as well, always the same error.

How can this be fixed?

I also tried mednafen as an alternative emulator, but when I open the ROM, there's nothing but a blank white screen.

Can anyone help?