Hello Ross
Thank you for helping me find it, the soft_build and soft_version is 10800 and 1.8.4 respectively.  I'm a bit nervous as to what I should put in there

The previous version and build were "version: 1.8.3 build: 10600".

This is also a helpful guide for a failed installation. It was from a previous version, but still applies.
https://developers.oxwall.com/forum/topic/44433

Thank you all for your help, and I'm sorry for taking so long to respond but unfortunately it didn't work.  I've updated to version 1.8.4 without a hitch but it hasn't made any difference to the cron error message.  I'm not sure what to try next...

Have you tried to disable all 3rd party plugins and see if you still get those error messages? 

I have now tried turning off all 3rd party plugins without success, still the same error message every hour.

Can you pm me your Cpanel access details, we'll take a look at the issue?

Thank you Ross, hopefully you've received the credentials, let me know if you haven't

I need admin access details as well, please send. 

Do you mean to the oxwall site?

Yes. Ross will need to site admin credentials to check your site. Sen it to him via PM. Don't post them here.

Okay, hopefully you got the credentials.  Let me know if you need anything else.

Madeleine, 

Do you receive these errors to your e-mail or in the error logs somewhere? 

If it is email, can I have access details to that email as well, please.