Unrecognized Guid Format Error in Asp. Net?

Hello all I am facing this problem in asp.net project . "System.FormatException: Unrecognized Guid format. at System.Guid.GuidResult.SetFailure(ParseFailureKind failure, String failureMessageID, Object failureMessageFormatArgument, String failureArgumentName, Exception innerException) at System.Guid.TryParseGuid(String g, GuidStyles flags, GuidResult& result) at System.Guid..ctor(String g) at UserAuthentication.HumanResources.ViewAllJobs() in HumanResources.cs:line 105"

my code and store procedure for HumanResource.cs is as follows First one is HumanResource code second is store procedure

       public static List<HumanResources> ViewAllJobs()
    {
        SqlConnection conn = new       SqlConnection(ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString);
        SqlCommand cmd = new SqlCommand("spHumanResourcesViewAllJobs", conn);
        cmd.CommandType = CommandType.StoredProcedure;
        List<HumanResources> jobs = new List<HumanResources>();
        try
        {
            conn.Open();
            SqlDataReader rdr = cmd.ExecuteReader();
            while (rdr.Read())
            {
                HumanResources hr = new HumanResources();
                hr.jobTitle = rdr["JobTitle"].ToString();

               Guid guid = new Guid(rdr["Guid"].ToString());
                hr.guid = guid;
                jobs.Add(hr);
            }
        }
        catch (Exception ex)
        {
            throw new Exception(ex.ToString());
        }
        finally
        {
            cmd.Dispose();
            conn.Close();
        }
        return jobs;
    }


             Store Procedure:
                 CREATE PROCEDURE spHumanResourcesViewAllJobs 
         AS
           BEGIN

SET NOCOUNT ON;


SELECT Guid,JobTitle
FROM HR
WHERE Active=1

END GO