Receiver File (FTP) Channel error

Hello Experts,

      We have a IDOC- FILE scenario in using PI 7.1. Configured receiver File Adapter with Transport Protocol : FTP and used Connection Security too.

      But whenever I am triggering and IDoc, getting the channel error:

     "File processing failed with Error when getting an FTP connection from connection pool:                     com.sap.aii.af.lib.util.concurrent.ResourcePoolException: Unable to create new pooled resource: FTPEx: Control               connection prematurely closed by server"

      I have also tried using data connection both Active and Passive.

      Please give your valuable feedback to solve this issue, bit urgent.

      Many thanks in advance Gurus...

Thanks

Ravi.