That item does not exist. It may have been removed by the author

Question

I'm trying to submit a guide to steam, but when I complete the very first step and press Continue I see the error message:

Error
Sorry!
An error was encountered while processing your request:
That item does not exist. It may have been removed by the author.

Here's a link to the Steam Community home page.

I tried the game client and the browser (Chrome).
I tried this under another account. Result is the same.

I can find a lot of posts about this error in google, but none of them have reasons and solutions/workarounds described. So those who know - please tell me what are the reasons and a workaround?

Answer 1

I've found a work around.

For some reason, Steam didn't like and didn't want to upload the image I used in that guide (I have no idea why. It was .jpg image 255x255). I used another similar image - and it worked. Than I reformatted the initial image to .png, and it worked with it as well.