Errors in admin when creating new Meta Box

I have 5-6 working Meta Boxes which work great. Today I wanted to add a new Meta Box. When I save the new Meta Box, I get two php errors at the top of the screen. I've taken screenshots showing what appears.

This is what is shown after giving the new Meta Box a name and clicking "save":
https://www.dropbox.com/s/ufygjvnfyb8hee3/error%20on%20save%20of%20new%20meta%20box.png?dl=0

This is what is shown after clicking the "save" button a second time:
https://www.dropbox.com/s/3iw5ducmaltxj2m/error%20after%20re-saving%20newly%20created%20meta%20box.png?dl=0

This is what is shown after viewing the list of Meta Boxes and clicking "trash" on this newly created Meta Box:
https://www.dropbox.com/s/e8gb5h0ig6kjn05/errors%20after%20trashing%20newly%20created%20meta%20box.png?dl=0