Alright, the error popped up because of an error in the file path (fileone or filetwo in the code).
Silly mistake made frustrating by a misleading error message.
However, I have these observations:
model.import and model.export have a second parameter which suppresses the summary window.
This works exporting, and importing skp files, but does not suppress the summary for dwg files. So the user must click on the OK button for every file which is imported.
model.save does not function as the application's file:saveas command, in that the open skp file does not assume the name of the saved file. model.save functions more like file:save a copy as.
These two points, along with the lack of a method to close a file (have I missed it?) makes automating any sort of batch processing difficult. Perhaps its intentional, but it limiting for a scripting language.