Attempt to restore deleted folder to WD external hard drive fails

I have a WD 1TB My Passport Portable External Hard Drive - USB 3.0 - WDBYNN0010BYL-WESN.

When I accidentally ? deleted a folder from the hard drive, I went to restore it from the Recycle Bin, but I got the following message:

There is not enough space on WD Unlocker. You need an additional 28.9 GB to copy these files.

Space free: 0 bytes
Total size 8.06 MB

If the folder was deleted from the hard drive in the first place, how could there not be enough space on that hard drive? There is nothing else on that drive except administrative type files.