Email Designer issue

I cannot open Email Designer. When I click on the button a new window opens with the following error:

If you need translation it says something like: Critical error occurred on this page. Check your admin inbox for instructions. If the issue persists, check the support forum.

I just upgraded to premium, but I was able to use the other new features except this. Also there were no email came through. I checked the Junk folder as well. I use Chrome, but I tried to launch Email Designer in Edge and it gives the same error. Could someone please assist?

Many thanks in advance!