Hello Sean, Espionage is protecting data by copying the data into encrypted disk images. The name of the disk image is randomly generated. The location of the disk image is determined in two ways: if you are protecting a folder which resides on your boot disk, then we will assume that the folder layout is standard OS X and will expect that there is a Library/Application Support present, so we create there our com.taoeffect.Espionage3 folder, and inside of it a Data subfolder and we put all the disk images there without asking you anything. However, if you are protecting a folder which is on an external drive, then we will assume that you do not want to put the disk image on your boot disk, but instead onto that external disk, but as we do not know the folder structure there, we will ask you where do you want to save it.
That being said, I suppose you were protecting a folder which was on your LaCie drive and when asked where to save it, you choose the root folder of the LaCie drive.
I assume you were using this folder before migration and it worked fine.
Now you say: "understood that I needed to copy the folder Library->Application Support->com.taoeffect.Espionage3 to the same location on the new computer. I did this and managed to successfully unlock the folder. Everything looked good,"
so did you try to unlock that folder which was on LaCie drive or not?
The problem is very simple to describe: in Espionage database, the folder you are trying to unlock has a recorded reference to the disk image /volumes/LaCie/F7355OF3-2B6E-473F-92EF-D31AA4EAAD12.sparebundle
If the disk image was moved, Espionage lost the reference, but this is easy to fix as long as you can find this disk image somewhere else.
If the disk image does not exist any more, then there is nothing Espionage can do.
Whether you modified the LaCie drive or not, I cannot tell, it is just a fact that the disk image was there once, and not it is not.
So as long as you can locate the disk image, we can fix this.
Rgds
Zsolt