Hi. I copied and pasted your XML and code into a new Access database file, and it worked fine.
Like you said, since you're using Callbacks, I had to add a reference to the Office 16.0 Object Library.
Otherwise, when I click on any of the items on the Ribbon, all I get are the messages from your error handler saying I don't have the object I'm trying to open, which means the Ribbon items are working as intended.
You could try what I did. Copy and paste the XML and code you posted in a new Access file and try it out.
Oh, by the way, you'll have to delete the semicolon at the end of the XML schema line. Not sure why you have one in there.
Let us know how it goes...