TWRP: update of V3.0.2-4 ends with error "(Not a directory)"

[Guest _Micha_]

Hi, I'm trying to update my installed and working TWRP 3.0.2-4 as described:

TWRP Install (Requires TWRP 2.8.4 or higher already installed):
Download the latest TWRP image file (.img) from the download link and boot TWRP. Go to install and 
find and select the Images... button. Browse to the image that you downloaded and select it. Choose 
recovery and swipe to flash.

I'm getting always the following command prompt output displayed, inclusive twice the same opening error: 

Quote

[IMAGE FLASH STARTED]
Image to flash: '/recovery/twrp.img'
Calculating restore details...
Error opening: '/recovery/twrp.img/' (Not a directory)
Error opening: '/recovery/twrp.img/' (Not a directory)

The errors make sense because the last slash (/) is wrong. What can I do to overcome this? I already tried different file names and file locations inclusive my SD-card.

Thanks!

Edited April 11, 2020 by _Micha_
title corrected