Hi David,
I had an issue migrating from 3.5 to 4.0 and this thread helped me, but it was the video that did it. My old database folder had a name like: xxxx.graphdb and the period was causing problems. After I pointed to my old database(with the period in the folder name) in the .conf file, it went through the six step process of upgrading successfully, but then in the browser none of my nodes were visible, and I couldn't figure out why.... until I saw the video and took the period out 
The period is still mentioned here as part of a valid db name: Administration and configuration - Operations Manual
and there's nothing about a valid name mentioned in the upgrade instructions of the Operations Manual(Upgrade a single instance to a 4.x patch release - Upgrade and Migration Guide). Could information about what makes a valid name be added/fixed in both locations? Thanks a lot for the video! :)
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