A user reported issues with Shadowbox JS plugin showing error messages in the dashboard.  I was able to replicate the issues and researched them. The research showed that the plugin had fallen out of support with the author.

In these instances, we do not attempt to take over support for the plugins that are out of support; we remove them from the server.

If you are interested in finding a replacement for the Shadowbox JS plugin, please let us know in the comments or contact me directly.