C＃ - ＆＃39;不支持给定路径的格式。＆＃39;

Question

private void saveStudent<T>(string filePath, T objectToWrite) 
{
  stream = File.OpenWrite(filePath); **//Error is here**
  var binaryData = new System.Runtime.Serialization.Formatters.Binary.BinaryFormatter();
  binaryData.Serialize(stream, objectToWrite);
  stream.Close();
}