I don't know if this is just a problem for me, but in case it has general applicability, I installed TTax2018 today and attempted to import from QD2017. It failed. When I started QD2017, I got an update (now showing R18.6). After I closed QD2017 and restarted it I was able to import. I'm guessing the update required some sort of file change that wasn't done until I saved my QDF file.
scott s. .