Sorry for the earlier cross-post: the problem was similar so I just added my dilemma: I should have started a new post.

I recently purchased Garritan Personal Orchestra 5 to run on my MacBook Pro running High Sierra. Here are the order of events:

-- installed GPO5

-- as suggested, attempted to update to the most recent version of the Aria Player, but apparently already have that version (1872) installed

-- Ran Aria player: attempted to load an existing midi file, created by MuseScore 3. According to the Aria Player page https://usermanuals.garritan.com/GPO5/Content/aria_player.htm  this should be possible: "The standalone ARIA Player also features a MIDI and audio recording system located on the bottom of the screen. With these controls, you can load existing MIDI files for the ARIA Player to play back using Garritan samples. You can also record yourself playing live." However, the midi file was greyed out and could not be selected when I went to (Menu) File -> Open and navigated to the folder with my midi files.

-- installed Garageband 10.3.2. The above midi file will open in Garageband and play. However, Garageband cannot find or load the Aria Player plugin. Followed the instructions here:

https://usermanuals.garritan.com/GarritanIntegration/Default.htm#garageband.htm

It says:

"To find the ARIA player plug-in: Installing your Garritan library will make the ARIA player available in Garage Band automatically."

Garage Band fails to find the Aria player and the instrument library is not available, either, following the steps outlined here:

https://www.garritan.com/blog/garritan-in-garageband/

Incidentally, that blog post is from 2013, so I wonder if the instructions might no longer be valid.

Please advise.