Hello, I tested it, it seems to be working fine with folders which are on the local/startup volume.
If the folder is on an external volume like USB stick or disk, then there seems to be a problem with locking the folder, it reports constantly that it is in use even if all files are closed, and even if I quit Espionage.
You have to force eject the volume in the finder, this will lock the folder. It seems it is just a logical problem, no data should be damaged during this, but in spite of that, we will surely look into this.
Cheers
Zsolt