I have used Recuva successfully before without difficulty. This time, I receive an error requiring 1,780GB of disk space to recover <1GB of a deep scan, Documents only. The drive I am recovering is 1TB.
Recuva is looking at all the deleted files and calculating the total of how much space each one used to take up.
As it's likely that some of them have been overwritten then that total can add up to more space than is actually on the disc that you are recovering from.
So some of the files found can be ignored, see below.
You could use a larger drive to recover to, (one with over 1,780GB), or could try to do the recovery in smaller stages rather than all the files at once
As said above some of the files found can probably be ignored as they have been overwritten, see this for some hints/tips:
My great-great grandfather came to the USA from Cumbria, leaving Lake Windemere behind! I discovered there were four .pdf's that were over 460BG each, so I omitted them from the recovery. I proceeded with the recovery, choosing only files in "Excellent" states, and most of those either open blank pages or produce errors, refusing to open.