Every time a post is made I receive the following error on our site, but if you refresh the post is there. I've attached a screenshot of the error.
This is general error, this says nothing. There is no any way to detect the reason of this error, this error has hundreds of reasons. If you don't have important data, I'd recommend Uninstall (not deactivate) wpForo then delete it then search and install it again.
If it doesn't help start with plugins, deactivate all those, delete cache and test it. Then change theme to the default WP theme and test it again. This is the only way to find the problem-maker.