Ham Radio Deluxe 6.4.0.646 was released earlier today (18th April 2017) and immediately I found an issue with it. I noticed during installation a message saying "Microsoft Access 2007 is being uninstalled". There were no questions asked it just did it.
The end result was that no databases (logbooks) could be opened nor new ones created. The simple solution to this is to reinstall the Microsoft Access 2007 Runtime. You did keep that copy you had didn't you? If you can't find it don't worry as there is a link in the FAQs section of the Ham Radio Deluxe LLC website.
Here it is
https://tickets.hrdsoftwarellc.com/kb/faq.php?id=114
or go straight to Microsoft Website to download it yourself.
https://www.microsoft.com/en-gb/download/details.aspx?id=4438
After installation the logbooks return.