After completing an upgrade of the forum software on my site, I received a message stating that 3 applications and 1 plugin was disabled. I then clicked to go to the forum and am now receiving a error:

An error occurred (500 Error)
We're sorry, but a temporary technical error has occurred which means we cannot display this site right now.

You can try again by clicking the button below, or try again later.

Try again

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Is there anything you can do to help me with this?

Thank you.

Try using recovery mode to disable all third party applications. 
 

Once disabled, you can login to the ACP and enable applications one by one to find your culprit. 

I see your site appears to be online currently. Please let us know if you are still experiencing issues, and we can then take a look for you.