I updated to LR6 a couple of weeks ago. I was surprised it didn't remove LR5 automatically.
When I inserted a memory card, my PC started LR5 for the import. I changed Autoplay to LR6 and set LR5 not to import, but it still kept starting LR5 on card insertion.
I uninstalled LR5 through the Control Panel. Now I get the error "Application not found" both when inserting a card and when right-clicking the drive and selecting Open Autoplay ... then 'Adobe Photoshop Lightroom 6.0 64'.
In Control Panel, Autoplay for Camera Storage > Memory Card is set to 'Adobe Photoshop Lightroom 6.0 64'.
LR6 is running happily on my PC.
Anyone any ideas? Many thx.