The RSA key used by 'SolarWinds SFTP & SCP Server' is too small: 1024 < minimum 2048 bits. Can 'SolarWinds SFTP & SCP Server' be configured to use an RSA key length of 2048 bits?
Create RSA key (I used puttygen and exported as OpenSSH key format) and save to C:\programdata\SolarWinds\sftp.rsa