File name too long for the recycle bin

I want to backup my computer on an external hard drive, which must be clean before the backup.

There is one folder that I cannot delete. It is a folder with many subfolders. I cannot access the files in any of these subfolders.

The message I get is:

Do want to permanently delete this folder?
The folder contains items whose names are too long for the recycle bin.

How can I get past this? Any help will be much appreciated.

Hanna 1 suggested the fastest and easiest fix, just format the external drive.