Hi,
Just tried your demo and it seems to work fine. I get your custom error message. However:
I did some investigating and i found out that the reason i am getting the "~interruppted" error message is because the file is empty. If i try and upload a file which is not empty but of the wrong type, i get a message that says the file is of the wrong type (in your demo and my solution)
In my test, i used an empty .txt. I tried it with your demo and i also got the "~interruppted" error message.
Hope this helps,
Antony