This might be the case. As I said in the orginal post: 'Every other pattern suggested works.'. I can use colons as a separator for example. I wondered if I did something wrong as backslash is the most natural separator here. Moreover the error message mentions the user id in the correct form, i.e. CORP\User, stating that the user id is invalid and not a character used. If the message is the response from the API that might mean that the SDK is not at fault here.