If the method using the SL Login ("Import from live inventory") doesn't work, try "Import from cache file" instead. That method also doesn't require a password, so it is also safer.
You can also use it while you are logged in, while "Import from live inventory" requires you to be logged out. However, if you did any changes to your inventory that are relevant to the import, you'll still want to log out so that the cache file reflects your changes.
If you experience problems with the "Import from cache file" method, try importing fewer items at once.
If the import still doesn't work, please reach out to me (Carlyle Theas), so I can check if there is a bug and I can fix it or help you further.