Hi there paige,

Thanks for reaching out! First, please make sure you have followed the installation guide completely. The message not unequivocal, pointing at two possible trouble sources.

First, it may have to do with (well, obviously) navbar ref being a string, as this practice is being depreciated in newer versions of React. This case scenario issue is being taken care of as we speak, and to fix it locally, please visit the MDB React node module (node_modules/mdbreact/src/components/Navbar.js) and make sure there is no string ref (i.e. ref='navbar' or ref=this.state.navbar, whereas in state you would have something like navbar: 'navbar'). Deleting these (or replacing them with a ref function, if you must) should solve the issue.

The other case scenario is more complex, as it involves having conflicting React versions installed simultaneously. It would be helpful to know what version of React you are using in your project - for that you can simply compare package.json files of the project and of 'mdbreact'. If they differ, it might require manual update of either of packages.

Hope it helps!

With Best Regards,
Kuba