Hi Cliff, thank you for trying to help,
I’d already deactivated all plugins except Beaverbuilder that without i cant use the widget at all and had tried a different theme.
I’ve left theme Twenty Seventeen on for you to see this and created a test page here
http://ca4.d48.myftpupload.com/test-calendar/
I’ve tried both free and pro versions of Beaverbuilder and both give the same error with the new 4.4.19 Eventscalendar but both work with 4.2.5 that we have on the live site
https://sandown.school/test-calendar/
Bit of a puzzle this one