i have problem with ftp

[joximu]

ok, looks better...

so, you can login via ftp and the customers cannot?

mostly it's the unconvenient username which ispcp needs.
ftp-user@domain.tld - as created in the ispcp panel...

You can see all ftp users in the mysql table (ispcp.ftp_users).

If this is not the reason then I think you need to debug the ftp session.
Stop proftpd, start it manually: proftpd -d -n 5
let the client login and see what's written on the console... (stop with ctrl-c)

/J