Thanks for your reply!
The converter is truly a fantastic tool so I can't really grumble that debian doesn't fall in to the category of supported distros, especially when I'm still able to have a working VM out of our physical Debian server. At this point this trouble shooting is more about satisfying my own curiosity rather than our production depending on it. And of course it's prettier when there isn't a big fat X with FAILED message on the screen after the job is done ; )
That being said I tried your suggestion and made a file '/etc/lsb-release' and wrote following lines in it:
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=16.04
DISTRIB_CODENAME=xenial
DISTRIB_DESCRIPTION="Ubuntu 16.04.2 LTS"
I encountered the same error, so it seems like it's still not recognized correclty. Do the contents in my /etc/lsb-release file look correct?
I'll attach the log file here just in case.