After a PAC controller has connected to an FTP server and remained idle longer than the server allows, the server can close the connection due to inactivity.
Each client FTP session that an FTP server closes due to inactivity may use up one of the controller's TCP/IP sockets. When the controller doesn't have any TCP/IP sockets available for a new connection, it refuses ALL subsequent communications requests. (For example, it would refuse requests from systems like PAC Manager, PAC Control, PAC Display, PAC Terminal, OptoOPCServer, a Modbus/TCP Master, or a SCADA package.)
When the controller is in this state, the only way to recover is to cycle power to the controller.
Either make sure your strategy communicates often enough to prevent the FTP server from closing the connection due to inactivity, or use strategy logic to close the FTP connection if there isn't a need to communicate within the FTP server's idle time-out setting.
Opto 22 has resolved this issue.