I have the DS-2400.
Hi,
Try importing the file again (not copying and pasting, but importing), and then looking in the "Finished folder." When I cannot see a folder this is where I have always found them--I have never figured out why this happens and the company I get my files from cannot figure it out either, but that is where they have been found. If you find your file there, you need to right click on the actual voice file and it will turn "blue," select "move the folder" to A,B,C,D, or E. Sometimes once you select the folder you want the voice file to go to it will just go right there, other times there will be a second step in the process where it asks you to click, finished, unfinished, pending, or cancel job. You need to check "unfinished" before the job will transfer to the folder you have selected.
I hope the above helps, as it has been the only solution I have found.