I just had the same issue. Because you mentioned about Cura 2.6.2, I was able to find a workaround for my problem. Hope this helps you as well, if you haven't already figured it out.
This happens only for the 'custom printer' profile. If you select any of the existing machines included in the software, you won't get this error. I tried changing the 'machine settings' of my new custom machine, but no luck.
But the custom machines which I had added a long time ago in the previous versions of Cura (which then were automatically migrated to the newer version when I installed one) were still working fine. I was using Cura 3.0, I tried Cura 2.7 but got same error.
Then I downloaded Cura 2.6.2 and it worked fine!
So the workaround is, create your custom machine profile in Cura 2.6.2 and then install the latest version. The new version will automatically import the profiles from 2.6.2 and they work perfectly fine with all the latest features!
But this is just a workaround and I hope the Cura team fixes this issue. Can't keep uninstalling newer version simply to add a machine profile and then install the new version again.