"Access is denied" when sending an email from CRM 2016 on-premise

Hi there,

we have a 2015 CRM On-Premise that sends out emails just fine.

We have a 2016 version of the same organization that we created.

When I create an email activity, fill it out and click Send, first I get the box telling me "your changes have not been saved" (??)

When I click Cancel, I get "Access is denied", and when i download the log file it complains that you "Cannot update parties unless email is in draft status."

(Sometimes it complains about the subject/description...)

If I click OK, it sends out the email....

Any ideas why this is happening?

I have tried it with the infamous "use legacy form rendering" set to yes and no - same behaviour.

Any assistance appreciated.

Thanks, Kevin