Packages that used to work fine have suddenly started failing. These packages use the SFTP task.
Security algorithms are improved and changed regularly. It is likely that the server which you are attempting to connect to has been updated to enforce the use of these newer algorithms. If you are using an older version of SSIS+, then these newer algorithms didn't exist when that version of the SFTP Task was released.
To update your version of the SFTP Task, uninstall your current version of SSIS+ and upgrade to the newest SSIS+ release. To download, go to the Download menu on the COZYROC website and fill out the form. You will receive an email with a download link.
If you don’t mind going in and updating your packages, you may want to start using the File Transfer task in place of the SFTP task, which has been deprecated. You'll be able to accomplish even more with this new task.