ftp authentication fails

[fooboo]

I have been using ISPConfig for a while and I have had a number of working ftp accounts pointing at various sites.

The accounts were still working yesterday but today for some reason they stopped authenticating. I get a "530 Login authentication failed" message using saved account details that were working fine yesterday and if I use ISPConfig to setup a brand new user those details get the same error message.

The only thing I have done involving user accounts since yesterday is added an IP to mysql to allow a user to administer a couple of databases remotely.

Can this affect the ftp accounts?
Is there something I can try to get them working again? I definitely have the right connection details.