Sorry for the late reply for weekend.
I tried with admin account and working.
But i could not login using subscriber account, so i could not test that. Can you please check that you can login with subscriber account you provided me? It is showing by cookies is blocked which is not. I tried with multiple browser (Safari, chrome, firefox) and showing same error message.
I had another look, and the error message is gone, the subscriber role can now send messages.
Not sure why it works now.
Perhaps it had to do with another plugin that was causing conflicts with some other plugins, too, and for which I just installed an updated version.
Anyway, the issue is gone.
Today the same thing happened to me again, and I was able to figure out the root cause.
For some reason there was an additional Subscriber role assigned to the Admin.
Taking it out, and it was working again.