Unsuspicious Wrote: Disable all of your plugins and re-enable them one by one; keep refreshing the thread every time you re-enable one, until the 500 error occurs again.
Then you know what plugin is causing it, or whether a plugin is actually causing it.
It would be advised to make a backup of your forum, then instead of disabling them, the codes still in the templates so uninstall them one by one like above^ but once you get to the plugin, load up the backup and uninstall that one plugin... yes it takes a bit more time but it's more efficient
Not really, the code in the templates would just be blank variables, seeing as the plugins would be deactivated and wouldn't be filling the variables with anything.