Try to change type of ScoreIfNoMatch, like this:
public class MatrixModel
{
public string S1 { get; set; }
public string S2 { get; set; }
public string S3 { get; set; }
public string S4 { get; set; }
public string S5 { get; set; }
public string S6 { get; set; }
public string S7 { get; set; }
public string S8 { get; set; }
public string S9 { get; set; }
public string S10 { get; set; }
// the type should be string
public string ScoreIfNoMatch { get; set; }
}