Common 421 errors include:
Error 421 Service not available, closing control connection.
Error 421 User limit reached
Error 421 You are not authorized to make the connection
Error 421 Max connections reached
Error 421 Max connections exceeded
You can receive a 421 error if the FTP server you are connected to limits the total number of connections available or limits the connections available to one user. To clear the error, remove items from the Queue Pane and make sure only one instance of CuteFTP is running.
To remove items from the Queue Pane
Sometimes the Queue Pane can become cluttered with unfinished transfers. To clear the queue, right-click inside the Queue Pane, then click Remove All.
To verify only one instance of CuteFTP is running on your system.
Right-click on the Windows Task bar, then click Task Manager.
On the Applications tab, view the list of running tasks to determine if CuteFTP is listed more than once.
If more than one instance is listed, click one of them, then click End Task.