Red5Pro: Error: Could not find or load main class Playground.red5pro

[AGSTRANGER]

I am getting started with red5pro.
I downloaded the server files from here and I am following this tutorial for the installation on Linux.

I have unzipped the file using this command:

sudo unzip red5pro-server-us-xxxxxxx.zip

Then I added these permissions:

sudo chmod +x *.sh

Then I tried to run the server:

sudo ./red5.sh

But, I keep getting this error:

Running on Linux
Starting Red5
Error: Could not find or load main class Playground.red5pro

I thought this is a problem with Java version as red5pro requires at least java8, so I run this command:

java -version

And I got this:

openjdk version "9-internal" OpenJDK Runtime Environment (build
9-internal+0-2016-04-14-195246.buildd.src)

But, I still get the same error.