Uninstall Logbook Pro from the Windows Control Panel Add/Remove programs.
Reinstall 1.9 that you downloaded. If it doesn't prompt 'Install Logbook Pro 1.9' when you double click the .exe, then you don't have the 1.9 installer. You can download it from www.logbookpro.com and you only need the lbproNoMSI.exe version.
However, I keep my data and Back-Ups in a different folder away from the LogBook Pro folder. I made duplicate copies of the data prior to trashing Logbook Pro. Then, I re-installed using the downloaded updat and started it up....no problem!!
I HIGHLY recommend separating your data out of the application folder.