OK I tried to vote again.
My thinking was if my original one had been accepted it would reject it and tell me I had already voted. If not I should get the error message that you did.
I got the error message so I guess I likely did the first time too but just left the site before I noticed it. I’m sure Martin will sort it out on Monday. :-)

The early bird gets the worm but its the second mouse that gets the cheese.