该错误通常是因为应用未被授权访问当前用户的信息而导致的。添加适当的权限后，问题应该得到解决。以下是使用Graph API获取当前用户信息的示例代码：

var authResult = await cca.AcquireTokenByAuthorizationCode(scopes, authorizationCode)
      .ExecuteAsync();
var graphClient = new GraphServiceClient(
      new DelegateAuthenticationProvider(
      async (requestMessage) => {
            requestMessage.Headers.Authorization =
                  new AuthenticationHeaderValue("Bearer", authResult.AccessToken);
      }));
var user = await graphClient.Me.Request().GetAsync();

如果您使用的是Rest Client，可以尝试以下代码片段：

var httpClient = new HttpClient { BaseAddress = new Uri("https://graph.microsoft.com/") };
httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", "[YOUR_TOKEN]");
var response = await httpClient.GetAsync("v1.0/me");
var content = await response.Content.ReadAsStringAsync();