请帮助， 尝试访问API端点时出现以下错误：
Compiler Error Message: CS0433: The type 'MediaTypeHeaderValue' exists in both 'System.Net.Http, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' and 'System.Net.Http, Version=4.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'