When starting the DXF job on a multisheet drawing, on the Export-Document commandlet the Inventor dialog "Save Copy As" shows up. This happens only on multisheet drawings.
One possible reason for this issue is that there already are copies of the file in the directory where Export-Document tries to export the file. If the Clean-Up commandlet didn't get executed you might experience this issue. The DXF files do not get overwritten when executing the job again.
Delete the files from the local DXF location or make sure they always get deleted when executing the DXF job. The default location in the powerJobs sample jobs is "C:\Temp\filename"