Join Page blank after upgrade

Hi everyone! I'm at a loss. I completely upgraded my site last week, and today, I went to the Join Page, and it is completely blank. No menu, no text, page source is empty, no footer. Nothing. I don't understand.

I just fully upgraded all the way to the most current version from 7.1.3 to 7.3.3 (yes, long overdue, but changes to the Facebook API forced me to upgrade, and so I did!)

I have tried replacing the join file and I made sure the bxdol and basetempl join pages are correct and were overwritten. Near as I can figure it, it is failing before loading the page template. Neither the pop up for join page nor the actual join page will load.

I checked my admin settings for the join page against the demo, and it looks correct. I am in template alt, not a custom template (I had to ditch my custom template for the upgrade)

Any help would be appreciated!

http://socialkicks.com/join.php

You have HTTP 500 error, it means Internal Server Error, you need to investigate web-server/php error log files for the particular error

Oh interesting! I found this error:

[10-Apr-2017 18:36:34 UTC] PHP Fatal error:  Call to undefined method BxMbpConfig::isDisableFreeJoin() in /home/socialki/public_html/modules/boonex/membership/classes/BxMbpResponse.php on line 28