There are multiple methods to convert a thread. What steps did you perform that led to this result? What is the URL where this error appears?
I am struggling to find a situation where it is logically possible for the convert count to be 0 at the same time as the vw_mod_import_type_ is not specified -- instead, I would expect either an "invalid item type" error or a "You do not have permission" error.
The blank usergroup setting is unrelated. Its phrase was given the wrong name. Fixed that in the next release.