[SOLVED] AppImages no longer working!

System: Slackware64-current - up to date.

I have a small number of packages installed as AppImages (I know, but at least one of them is ONLY available as an AppImage!)

They were working perfectly yesterday. Today, they are not! I get the following error box pop up if I try and run any of them:
Code:Cannot mount AppImage, please check your FUSE setup.
You might still be able to extract the contents of this AppImage
if you run it with the --appimage-extract option.
See https://github.com/AppImage/AppImageKit/wiki/FUSE
for more informationThe link to the Github repository doesn't help much with Slackware! Running it from the command prompt with --appimage-extract extracts it, but it still doesn't run.

Running from the command prompt without the --appimage-extract option gives:

Code:fusermount: failed to access mountpoint /tmp/.mount_UltimaOvZ0q9: Permission denied

Cannot mount AppImage, please check your FUSE setup.
You might still be able to extract the contents of this AppImage
if you run it with the --appimage-extract option.
See https://github.com/AppImage/AppImageKit/wiki/FUSE
for more information
open dir error: Transport endpoint is not connectedThe only things that have changed since they were working are: 1) 28th June updates applied. 2) Graphics card changed following a failure.

My AMD graphics card died, and I found an old NVidia one in my spares box, and fitted it. This got my system up and running again. I have not installed any NVidia drivers, so I guess I'm running Nouveau.

Any one got any ideas?

--
Pete