As of 09/23/2014, all QuickBooks Online SDK requests will be unable to connect to QuickBooks Online companies. You can read more about this migration in this 12/20/2013 blog post.
If you are still using a QuickBooks Online SDK request, you will receive the following response:
500 – General error building XML response. Exception from other package: org.xml.sax.SAXParseException: Element type “n.length” must be followed by either attribute specifications, “>” or “/>”
Here are some useful links if you need to migrate your QuickBooks Online SDK requests to QuickBooks Onliine REST API v3:
Forum: Migrate QB Online SDK to QB Online REST API v3
Ticket: Request specific migration support
Customers will need to click the “Connect to QuickBooks” button inside your app, and authorize(via OAuth) your app’s access to their QuickBooks Onlne data. Please see the following documentation for implementation details: Implement OAuth in your App