I am receiving this error back from CustomizableFlashTemplateService::addCustomizableFlashTemplate when connected with valid credentials and using a valid customizableFlashCreativeId and name.
Are there any undocumented (or just not very obvious) limits that I am running into, or did I find a bug? This is in V4 sandbox.
Resolution: This is a bug, in both V4 and V5, but the bug is only that the API returns the wrong error. The problem was caused by sending the parameter "customizableFlashCreativeId" instead of "customizableFlashCreativeID". Other API calls will return E1011: "A required field is missing or empty: xxxx". This one should as well.