Solved simply from another forum:
Usual scenarios we’ve seen are : (1) FTP users not appending the domain name at the end of the user name. Eg., using “myftpname” instead of “myftpname@domain.com”.
I can login to my automatically created ftp account, accountusername@domain.x10host.com but I created a new ftp account from x10Hosting Basic with 'other'@domain.x10host.com and specified a simple password. When I first click on ftp accounts the message box says 'This website does not have any...