That's because the NestedClass(appA42serviceManager.AppCallBack_createUser) cannot access the non-static, member bUserCreateOnSuccess_daniel declared in the OuterClass(appA42serviceManager). The members of the OuterClass(appA42serviceManager) are not directly available to the NestedClass(appA42serviceManager.AppCallBack_createUser). Well, then how can the NestedClass access the members of the containing class? This is how:
public void OnSuccess(object oResponse){
User user = (User)oResponse;
string sUserName = user.GetUserName();
switch(sUserName){
case "daniel":{
appA42serviceManager.bUserCreateOnSuccess_daniel = true;
}break;
}