Putty has a new version of their ppk or private keys.
This does not appear to be supported by Camel FTP jar library that Qvera Interface Engine uses for SFTP. We have found you can export it as an Open SSH key and it will work. Below are the steps to do this.
1. Download and install puttyGen version .76.
2. Use the Conversions menu "Import Key" and import your ppk file.
3. After Import select "Export OpenSSH key" and select a location for the new file.
4. In QIE point to the new file that is open SSH from step 3. See https://www.qvera.com/kb/index.php/1368/how-do-sftp-file-using-rsa-key-certificate-without-password?show=1368#q1368