Weird no free space error

Hello, I am trying to add an ebook from calibre to my Libra 2 device using OPDS Catalog and I get the following message.

"Could not save file to...No space left on device"

I also tried to change the default folder from SD to root, didn't helped. This is not the first time I am using this method to transfer files, didn't had problems in the past.

The file is an .epub approximately 15mb. I have 60gb+ free storage.

Thank you