Please try this:
After setting the new password, login to the control panel once to ensure FTP access is enabled. After that, you can attempt to reconnect to FTP with the new password.
Because the system is designed in such a way that when changing the pass or when creating an account, FTP is not allowed unless the control panel is first visited.
If everything is fine with that, then it is possible that some maintenance work is currently being carried out on the file server where your websites are located (home dir - volume XY)
so no entry is allowed during that process.