Ye thanks for all your help, its appreciated.
I realised there must be an upgrade gone wrong somewhere once I saw the referenced dll versions were wrong. So I deleted the server directory and did a fresh install from the manual server install package rather than the upgrade one.

Now its working fine  🙂 !

Thanks again Marco.

Marco,
Can you please confirm the letsencrypt renewal schedules are built into the SolidCP scheduler service?
Do we need to do anything regarding this or is it all built in?

Glad it's working now.

The renewal process is handled by the LetsEncrypt win Simple client.

It creates a windows task for renewals etc.

You won't need to configure a thing 🙂

Does it create a new scheduled task for each certificate? Or just one for all?

It is one scheduled task per server for all LE certificates.