If you have a free Google Domain Account or a recently updated paid account, you may need to login to Google to accept their new terms of service before uploading many sorts of files.
This does not apply to you if you have a simple free gmail account.
If you try to upload files and you have not accepted the new licence terms, you will get a "Server Rejected Error" or "(403) Access Denied".
If you wish to accept the new terms of service:
1. log into your Google Docs account using your web browser
2. read the new terms of service "Important changes to your Account" message from Google.
3. click "I accept. Continue to my account" button
You can now upload files to your account again.