Issue Setting Up PLEX

I recently installed OMV on a "new" server and everything is setup properly AFAIK, but I can't seem to get PLEX installed.

Here's the current issue I'm running into:

root@morty:~# apt-get update
(((Too much here to post)))
Err:18 https://dl.bintray.com/openmediavault-plugin-developers/arrakis {distribution}/{components} amd64 Packages
  404  Not Found
Ign:19 https://dl.bintray.com/openmediavault-plugin-developers/arrakis {distribution}/{components} all Packages
Ign:20 https://dl.bintray.com/openmediavault-plugin-developers/arrakis {distribution}/{components} Translation-en
Ign:21 https://dl.bintray.com/openmediavault-plugin-developers/arrakis {distribution}/{components} Translation-en_US
Ign:22 https://dl.bintray.com/openmediavault-plugin-developers/arrakis-plex {distribution}/{components} all Packages
Err:23 https://dl.bintray.com/openmediavault-plugin-developers/arrakis-plex {distribution}/{components} amd64 Packages
  404  Not Found
Ign:24 https://dl.bintray.com/openmediavault-plugin-developers/arrakis-plex {distribution}/{components} Translation-en
Ign:25 https://dl.bintray.com/openmediavault-plugin-developers/arrakis-plex {distribution}/{components} Translation-en_US
Exception ignored in: <function WeakValueDictionary.__init__.<locals>.remove at 0x7f0475ac6510>
Traceback (most recent call last):
  File "/usr/lib/python3.5/weakref.py", line 117, in remove
TypeError: 'NoneType' object is not callable
Exception ignored in: <function WeakValueDictionary.__init__.<locals>.remove at 0x7f0475ac6510>
Traceback (most recent call last):
  File "/usr/lib/python3.5/weakref.py", line 117, in remove
TypeError: 'NoneType' object is not callable
Reading package lists... Done
W: The repository 'https://dl.bintray.com/openmediavault-plugin-developers/arrakis {distribution} Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: The repository 'https://dl.bintray.com/openmediavault-plugin-developers/arrakis-plex {distribution} Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: Failed to fetch https://dl.bintray.com/openmediavault-plugin-developers/arrakis/dists/{distribution}/{components}/binary-amd64/Packages  404  Not Found
E: Failed to fetch https://dl.bintray.com/openmediavault-plugin-developers/arrakis-plex/dists/{distribution}/{components}/binary-amd64/Packages  404  Not Found
E: Some index files failed to download. They have been ignored, or old ones used instead.

Can anyone shed any insight?

Thanks!

cat: /etc/apt/sources.list.d/omv-extras-org.list: No such file or directory

I should mention a couple things that may be helpful.

First - For some reason I could not install OMV on a flash drive. I have two brand new, never-been-used 16GB Sandisk USB 3.0 capable flash drives that I tried and was intending to use (one as the primary, one as the backup) but despite detecting them both in the partitioning/installing portion of the setup process, it said they could not be partitioned. The OS is currently installed on a secondhand 250GB 7200 RPM Hitachi disk.

Second - Once in the web gui, almost every single time I save or apply a change, I get an error pop-up referring to my temp folder. If I try saving/applying again, there's a chance I'll get another pop-up referring to the same issue or a different issue (again referring to a file in the temporary folder) but if I keep trying, eventually the progress bar pops up and the change is applied. Not sure if this has something to do with the issue or not.

Unfortunately the only "manual change" that I've applied outside the web gui was done via ssh while logged into root:

echo "deb https://dl.bintray.com/openmediavault-plugin-developers/erasmus-plex {distribution} {components}" | sudo tee -a /etc/apt/sources.list

I did also add a commented line via nano in the sources.list file to indicate what that was.

Everything else was done as simply/automatically as possible via the installer or in the web gui.

dpkg -l | grep openm
grep -r bintray /etc/apt/*
returns...

root@morty:~# dpkg -l | grep openm
ii  openmediavault                   4.0.9-1                        all          openmediavault - The open network attached storage solution
ii  openmediavault-keyring           1.0                            all          GnuPG archive keys of the OpenMediaVault archive
root@morty:~# grep -r bintray /etc/apt/*
/etc/apt/sources.list:deb https://dl.bintray.com/openmediavault-plugin-developers/arrakis {distribution} {components}
/etc/apt/sources.list:deb https://dl.bintray.com/openmediavault-plugin-developers/arrakis-plex {distribution} {components}

Edit: FYI, I've reinstalled OMV once before the current installation and the previous installation had the same web GUI temp file pop-up errors without having changed a single thing. I first noticed it when I went to make the first change -- updating the admin password -- and it has been an issue ever since.

I apologize for my ignorance, I'm only just getting the hang of such things.

Thank you for your insight and assistance.

If I may, I'm not sure I follow when you speak of unreleased beta code? Are you talking about the PLEX plugin or the OMV installation I'm currently using?

To make my user experience as fluid and, hopefully, trouble-free as possible, do you recommend using OMV 3.x instead of 4.x?

An excellent response which answered a question I had not yet asked!

I was wondering if maybe the PLEX webgui might interfere with the OMV webgui but your answer just solved that for me. In fact, I was hoping/planning/intending on installing Docker and using that as a basis for several other applications I had hoped to host on my server. Excellent.

Thank you so much for your help! It's users like you that make the world of Linux less inhospitable and more inviting.

Cheers!