My synchronize pgm. can’t synch. my database, complaining that the internal
file “DEVONthink.dtBase:DEVONthink.lock” is locked. Any way around this?
Please be cautious – and best to have very limited expectations – about using synchronizing software with a DEVONthink database.
Do not expect synchronizing software to handle two-way synchronization of database files between two computers. The database has a monolithic structure that the synchronization software cannot understand. At best, 2-way synch will fail and nothing will happen; at worst, both databases will be ruined. Down the line – especially after the version 2 database is implemented – the potentials of synchronization for non-experts will be better. This topic has been discussed several times in the forum.
That said, I have used a synchronization program for 1-way only transfers of files, e.g. from a desktop to a portable. Usually, though, I just do a file transfer over my wireless network. 
And I do encourage use of backup software.
That file “DEVONthink.lock” is created by DT to protect the database in certain cases. If everything is OK, e.g. the Verify & Repair tool finds no problem, quit DEVONthink, open the DT Personal DEVONthink folder (in Applications Support). As you are using DT Pro, in the Finder select your database, click on the Actions button (cogwheel symbol, and tell it to display package contents. If that file is still there, it can be removed. (It’s possible that your synch software copied the database except for that ‘lock’ file; check your target to see if it’s there.)