I have recently upgraded to DNN 9 and despite being told by DNN on Facebook that there are no breaking changes in DNN 9, multiple modules are no longer working.

They both display correctly to the user, but the edit screens for both do not work, showing an error "Error: is currently unavailable. DotNetNuke.Services.Exceptions.ModuleLoadException: Unknown server tag 'dnn:dnngrid'."

This was not the case before upgrading to DNN 9 and nothing else has changed on the site.

How can I get those server tags to work again?