In my case, FileHelpers.dll was not present in my Putty Session Manager folder - probably because I was using putty tools that had been passed from hand to hand - someone apparently lost that dll over the years :) . I downloaded the latest official Putty Tools and 1. I found a FileHelpers.dll file in my PuTTY Session Managerfolder, and 2. Exporting Putty sessions to CSV from Putty Session Manager works fine now. Thanks for the tip above . -dave