SQL error when trying to save a record.

I have to check and save details of file(s) from a folder into a SQL server database. I am trying to do it but have some runtime error. Below is the code:

public async void PostValuesIntoDB()
        {
            DirectoryInfo info = new DirectoryInfo(path);           
            FileInfo[] fileInfos = info.GetFiles("*.trm");
            if (fileInfos != null || fileInfos.Length>0)
            {
                foreach (FileInfo fileInfo in fileInfos)
                {
                    RsbfileDetail detail = new RsbfileDetail();
                    detail.Filename = fileInfo.Name;
                    detail.FileUrl = fileInfo.FullName;
                    detail.FileType = fileInfo.Extension;                   
                    detail.CreatedDate = fileInfo.CreationTime;                   await _rSBRepository.Add(detail);
                }
            }

Below is the error that occurs at the highlighted line:

System.InvalidOperationException: 'Unable to track an instance of type 'RsbfileDetail' because it does not have a primary key. Only entity types with primary keys may be tracked.'

I have checked in my Database, which has a [RSBFileDetails] table with "[File_Reference_Id] [int] IDENTITY(1,1) NOT NULL" column as primary key.

My repository code is and fields are autogenerated: 

public interface IRSBRepository : IRepository<RsbfileDetail>
    {
        Task<RsbfileDetail> UploadFiles(string filename);
        public void GetNewFileFromFolderToDB();
        Task<string> Add(RsbfileDetail rsbfileDetail);
    }

RSBRepository.cs

public class RSBRepository : Repository<RsbfileDetail>, IRSBRepository
    {
        private readonly rsbsrdbContext _dbContext;        
        public RSBRepository(rsbsrdbContext dbContext) : base(dbContext)
        {
            _dbContext = dbContext;           
        }
        Task<RsbfileDetail> IRSBRepository.UploadFiles(string filename)
        {
            throw new NotImplementedException();
        }

        public async Task<string> Add(RsbfileDetail rsbfileDetail)
        {
            string dbresult = string.Empty;
            _dbContext.Add(rsbfileDetail);
            var response= await _dbContext.SaveChangesAsync();
            dbresult = response.ToString();

            return dbresult;
        }
        public void GetNewFileFromFolderToDB()
        {
            List<RsbfileDetail> result1 = new List<RsbfileDetail>();
            result1 = _dbContext.RsbfileDetails.Where(j => (j.Filename == "sample.txt")).ToList();       
            Console.WriteLine(result1);
        }        
    }

Can anyone help me solve this issue please