Probably an idiot, but… my database seems to be missing. Shifted from Personal to Pro, and (I think–it’s been a while) used to have database stored in Library > Application Support > DEVONthink. Which still holds a few files (DEVONthink-1.database), but Pro won’t open them. And can’t find any likely candidates anywhere else. Any ideas? I’m getting worried…
angus:
Unless you deleted it, your DT Pro database should be somewhere on your HD. The suffix is .dtBase, and you can search for that string.
What happens if you launch DT Pro, then press File > Open Recent and select the database?
If your DT Pro database has been deleted, you can still recover the data held in your DT Personal database. Here’s how:
Your original DT Personal database is intact. In the Finder, locate it and select (don’t open) the DEVONthink folder. Copy (Option-drag) it to another location, such as your Documents folder. Still in the Finder, select (don’t open) the copied DEVONthink folder and press Command-I to open the Info panel. In the Info Panel, rename the folder by adding the suffix “.dtBase” (without quotes). Press Return, then close the Info panel. You have converted your old DT Personal database to DT Pro. Double-click on the new database package to open it under DT Pro.
I suggest that, with your database open, you select File > Database properties, then check to make this your default database. It will then automatically open each time DT Pro is launched.
You should now find the database in your Documents folder in a ‘package’ format, ie. instead of a folder as before it now has the appearance of a single file with the DT icon. As I remember that opened automatically on first switching over though…
Thank you Bill for quick and perfect fix!! 
(Maybe my first emoticons. Wasn’t panicking too hard, but the relief is great.)