Hello pd1998,
If this was caused after an upgrade from pre-2.9 to 2.9 or newer, it's likely caused by the post_auth script still being a Python2 script while it should be Python3 now. Version 2.9 was rewritten to Python3. If you have this issue, fix that and reload the script and things should work again in that case.
To get Access Server working without your custom authentication post_auth script and get Access Server starting up again you can remove the post_auth script.
https://openvpn.net/vpn-server-resources/post-auth-programming-notes-and-examples/#removing-an-active-post_auth-script
Are you running latest version of Access Server, 2.11.3?
Can you share your custom post_auth script (without any sensitive details) here, or, if it is sensitive, can you submit it in a support ticket at
https://openvpn.net/support?
Kind regards,
Johan