I\'ve had success creating objects with POST and Content-Type application/xml
I\'ve also had success querying using Content-Type application/x-www-form-urlencoded wi
Do you get a 401 with the same request in the API Explorer?
http://ippblog.intuit.com/blog/2013/01/new-ipp-developer-tool-api-explorer.html
Also, are you using the static base URL or retrieving it at runtime?
https://ipp.developer.intuit.com/0010_Intuit_Partner_Platform/0050_Data_Services/0400_QuickBooks_Online/0100_Calling_Data_Services/0010_Getting_the_Base_URL
If you are using the static base URL, try switching to the runtime base URL to see if you still get the error.