Hi.
What menu do you have in the Arduino IDE to upload files?
Does it say “ESP8266 LittleFS Data Upload”?
Regards,
Sara

Correct

Hi again.
Do you have more information about the error?
Can you try installing the latest version of the LittleFS plugin if you haven’t already: https://github.com/earlephilhower/arduino-esp8266littlefs-plugin/blob/master/README.md?
Regards,
Sara

As per the ebook Build Web Servers esp32 esp8266, it goes through this progression.
install Arduino IDE – had it prior to ebook
install ESP8266 addons – board has been installed prior to ebook
setup to use LittleFS: get the latest code. I downloaded ESP8266LittleFS-2.6.0 I created this folder path as it did not exist: >/tools/ESP8266FS/tool/. I unzipped the .jar file to this location and started up the Arduino IDE. It then says to open a blank sketch and save it. I then went to that sketch, created a data folder and made a text file within it. I complied the sketch. I then changed the flash size to 4M (1M SPIFFS). After that, I hit the EPS8266 LittleFS Data Upload and I get the error in the compile window.
 

I did download this zip file but saw no mention of having to use it. arduino-esp8266littlefs-plugin-2.6.0

Hi again.
Can you tell me the complete path where you created the tools folder?
Regards,
Sara

Thanks for trying to help resolve this issue!

C:\Users\Stephen\Documents\Arduino\tools\ESP8266LittleFS\tool

Hi.
It seems that you did everything right.
I don’t know why it is not working as expected.
Meanwhile, I found an issue with that same error on the Plugin GitHub page. Maybe you can post your case there too. 
Here’s the link:
https://github.com/earlephilhower/arduino-esp8266littlefs-plugin/issues/15
I hope they can help you.
Otherwise, I recommend uninstalling everything, including your Arduino IDE installation, and start from the beginning.
Regards,
Sara

Hi Sara. I finally found the solution. I installed the core according to this website:
https://arduino-esp8266.readthedocs.io/en/latest/installing.html#using-git-version
Just thought I would share in case someone else asked a similar question

Hi.
That’s great!
I’m glad you found the solution, and thanks for sharing!
This can be useful for others too.
I’ll mark this issue as resolved. If you need further help, you just need to open a new question in our forum.
Regards,
Sara

Hi, I had the same problem. I tried installing the ESP8266 library V2.6.3 and that solved the problem.

Hi Edward.
Thanks for sharing your feedback.
It is probably some incompatibility with the ESP8266 add-on version.
Regards,
Sara

Seems to be OK with esp8266 board  version 3.02

Great!
This issue is closed now.