...
Unfortunately, the dropbox code Step 3 downloads from dropbox.com has an error and must be edited to fix. With We hope Dropbox will fix this in the future.
In the mean time, with PP running, type Alt-E to bring up Gedit. Then click Open. Then type Alt-Up Arrow. That takes the File Open dialog up one directory and you’ll see dropbox.py sitting there on the internal drive. Select it. Then go down to line 866 which should be this line:
...