Xamarin Workbooks crashing on "File...Open"

I'm trying to get started with Xamarin Workbooks 1.5. I run it and select "Console" and ".NET Framework" and then hit "Create Workbook". A new workbook is created. Then I select "File...Open". I get a busy cursor for a few seconds and then an error dialog: "Xamarin Workbooks has stopped working". I've uninstalled and reinstalled and get the same behavior. What could be going wrong here? Thank you in advance.

-L