Warning from Plugin

Hello, after updating some plugins on our site we got the following message and, for a time, were completely locked out of the site. We’re novice WordPress users in the process of learning more. I’m wondering if anyone would venture an explanation and set us off in the right direction to solving the issue.

For the moment we’ve disabled the custom menu wizard plugin, which has our site up and running. I’d like to be able to identify the underlying issue and repair it though. Thanks for any help you can offer.