Cannot access Admin portal

Question

Was able yesterday to access the admin portal, went into exchange admin and setup all accounts for MFA. Today I'm unable to access the portal, receiving:
Server Error in '/' Application.
Runtime Error
Description: An exception occurred while processing your request. Additionally, another exception occurred while executing the custom error page for the first exception. The request has been terminated.

Additionally, on my desktop Outlook app I can add my other exchange accounts but this one continually fails. I've followed recommendations of suspending AV, removing credentials, and setting server settings manually but it fails not able to establish a secure connection and then unable to establish an unsecure connection.
Thanks

Answer 1

Which version/CU of Exchange are you using?

Check the Event Log for any related errors.
Are you able to access ECP via https://localhost/ecp on the Exchange server?
Please try to remove and recreate the ECP virtual directory and see if it can be fixed.
If it doesn't work, It's suggested to run the "UpdateCAS.ps1" and “UpdateConfigFiles.ps1” script from the Exchange install directory scripts subfolder:

C:\Program Files\Microsoft\Exchange Server\V15\Bin>.\UpdateCas.ps1

C:\Program Files\Microsoft\Exchange Server\V15\Bin>.\UpdateConfigFiles.ps1

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