I am running the following command to get my encrypted obb file for apk expansion.
jobb -d /home/manoj/Desktop/Test -o main.1.com.example.helloworld.obb -k \
In my case, I solved the issue removing several hidden files...
My boss owns and works on MacOSX, me on Windows. So, when he passed it on and after opening the folder, I found several hidden files, such as .DS_Store and ._.DS_Store. Additionally, I found hidden temporary JPGs, for example if I had a file called image1.jpg I had another one .image1.jpg. So, eventually I deleted all of the hidden files.
And voilà!