Hi,
I suggest that you select the sub-folders of the main folder.
Or whatever level of granularity you want to work with.
What the app does is (roughly):
Given a folder, get the sizes of the first-level folder/files
Allocate them across the target disk(s) (recreating the whole tree)
An example
If you have a folder structure such as this:
- films
-- bluray
--- Movie1
--- Movie2
...
--- Movie 999
-- dvd
and select films, it will try to allocate bluray (which might be in the TB range) and dvd.
Unless you have an empty target disk, most likely it won't be able to allocate the bluray folder.
If you select films/bluray, it will try to allocate the individual MovieX's, which will be roughly 50GB each, and that is very likely to succeed.
The app depends on the user providing the "work unit" to operate on, to put it in other words.