I have an update from iFastNet about the situation.
The hardware on which these servers run suffered a file system corruption problem. iFastNet has worked hard to repair it and recover as much data as possible. Unfortunately, some data was permanently lost and could not be recovered. Accounts experiencing the 404 and FTP home directory errors have all lost their files.
Later today they plan to recreate the missing directories so it’s possible to login to FTP again.
We’re all sorry for the inconvenience caused.
This only affects website files. Everything else, including databases, are unaffected by this, and can be used to rebuild the site if necessary.