Try resetting the retroarch.cfg - the global configuration file - in \\retropie\configs\all. Replace it with the retroarch.cfg.rp-dist from the same folder.
However, if you used a remap/input override, this won't help.
@RumblinBuffalo Thanks again - I'll look at updating retroarch shortly. Although I'm concerned after reading that thread that it will remove/reset all my IPAC keyboard controller mappings, which took me a long time to get right initially.
ha, i just figured it out - in the Disk Control option in the retroarch menu (select+x), if i select Disk Cycle Tray Status it ejects the current disk, then i select Disk Image Append and i can select the .d64 file for the next disk! it appears the .m3u functionality isn't needed (or doesn't work anyway).
That's good advice. I have two cards that I alternate between when it's time to upgrade. It's intended as insurance to protect my time, but I've never actually had to go back to a previous card. As far as the difficulty of upgrading is concerned, I run 33 systems in RetroPie that are highly customized, as well as dual boot into an equally customized OSMC and it only ever takes about 30-40 minutes to upgrade and restore my settings back to where they were. Granted, even that amount of time can be hard to come by during a hectic week, but that's why God invented Sundays... well, you know, that and all the praising, but I doubt he's ever smited anyone for catching up on a little computer maintenance all the same.
@j-e-f-f I've never used the libretro one but for the standard vice I had to change the keyboard from symbolic to positional, not sure if that will help in your case as I don't recall having your issue but my other issues were solved with this change.