Hi,
Try these..
---> Make sure the FTP server is UP and running..
--> Specify Host name of the FTP server in file communication channel or IP address of the server?
--> Check whether the FTP user have all the access / FTP user locked?
--> Some times due less number of parallel connections at FTP server you may get this error.
Try to set the poolWaitingTime parameter in advanced tab of communication channel may help you to get rid of this error.
Please check with FTP team.
Regards
Bhargava Krishna