I think I've narrowed down what's causing the strange error message. However, you can login to your account without creating an FTP account anyway, by logging into FTP with your cPanel username and password.
I think that red bar should contain some text - perhaps it is being rendered incorrectly? Could you be so kind as to view the page source (perhaps right click on the red box and choose Inspect Element) and see if there's anything that stands out?
I have no issue with adding a FTP user with cPanel on x10hosting's free-hosting server [ xo3 = (old Level) - IP: 198.91.81.3 ]
it looks like you are using [ x10hosting Basic ] in your screen shot - try in cPanel - switch to cPanel at top of screen
Status: Resolving address of ftp.evasion.x10.mx
Status: Connecting to 198.91.81.3:21...
Status: Connection established, waiting for welcome message...
Response: 220---------- Welcome to Pure-FTPd [privsep] [TLS] ----------
Response: 220-You are user number 20 of 50 allowed.
Response: 220-Local time is now 22:21. Server port: 21.
Response: 220-This is a private system - No anonymous login
Response: 220-IPv6 connections are also welcome on this server.
Response: 220 You will be disconnected after 15 minutes of inactivity.
Command: USER evasionx
Response: 331 User evasionx OK. Password required
Command: PASS ********
Response: 530 Login authentication failed
Error: Critical error
Error: Could not connect to server