Welcome to the Community,
which system do you want to convert? Is it the one on which you installed the Converter? In this case you only need to install the Converter Client and select "This local machine" as the source. Also make sure you start the Converter "As Administrator" to avoid UAC related issues. If it's a remote system, you may want to consider disabling UAC on the system to convert, and use the system's local "Administrator" account to login.
André