If you are experiencing errors using the web services API you may find suggestions here.

• HTTP Error 429
  This error indicates that your application has been throttled by the rate limiting functionality. You will need to capture these errors and enable your application to retry the requests a short time later.
  
  
• HTTP Error 403 - "no, you can't"
  This error indicates that your action cannot be completed in BCDE, but this can be for a number of different reasons:
  • Is your web services key correct?
  • Is the timestamp on your requests correct?
  • Is the user your application is using able to perform the action if you log in through the front end and try manually? (e.g. is it an access rights or membership issue?