I installed mupen64plus and it worked fine with several ROMs. I then installed picodrive and VGBA, and mupen64plus stopped working. In the console it gave a segmentation fault. I had to delete .mupen64plus directory, uninstall and reinstall, now it works again. Not sure if picodrive or VGBA had anything to do with the error, but I can't think of anything else I did between mupen64plus working and not working. I also played around with the button configurations, but ROMs had loaded fine when using these.