Thanks for the reply s. I've been busy on other issues and haven't had time to come back here.
I have solved the issue of the following message in my new Access 2019 db; "Missing or broken Reference to file MSCAL.OCX v7, Fix the reverence".
I have several Office 2007 dbs running perfectly in 2019, all using the old calendar, which I/we thought was the culprit in one of my old dbs. I removed the calendar and all references to it and still the thing would not open in 2019.
After a bit of hair pulling, I opened a new db in 2019 and imported the tbls, qrys, forms & reports, one at a time. The idea was to see where the problem was. Here's the strange bit, everything worked with the exception of the old Switchboard. After making a new Switchboard in 2019, I now have the db up & running.
Thank you for your link to the new date picker, I think I'll have a look at it and maybe add it to my dbs over time.