Actually, it happens to me too when I try to do literally anything now...
When someone registers, the oops message appears, but the user is actually registered.
When sending message error is displayed, however on page reload, the reply was added.
The error message is not supposed to be there at all then.
Hope my extension didn't mess it up...
Edit: This issue only happens on my forum. I tried deleting cache, but that didn't help.